:root {
  color-scheme: light;
  --paper: #f4f1e9;
  --paper-raised: #fbfaf6;
  --paper-deep: #e8e3d7;
  --ink: #171914;
  --ink-soft: #5f625a;
  --ink-faint: #6f716a;
  --line: #d8d3c7;
  --line-strong: #bdb8ab;
  --math: #2855d9;
  --math-soft: #e8edff;
  --physics: #a8482d;
  --physics-soft: #f6e7df;
  --signal: #c9f24d;
  --success: #157347;
  --error: #b42318;
  --shadow: 0 18px 50px rgba(42, 38, 28, 0.09);
  --topbar-height: 72px;
  --sidebar-width: 248px;
  --radius-sm: 8px;
  --radius-md: 14px;
  --radius-lg: 22px;
  --display: "Newsreader", Georgia, serif;
  --sans: "Manrope", system-ui, sans-serif;
  --mono: "DM Mono", ui-monospace, monospace;
}

[data-theme="dark"] {
  color-scheme: dark;
  --paper: #151713;
  --paper-raised: #1e201b;
  --paper-deep: #272a23;
  --ink: #f1efe7;
  --ink-soft: #b7b9b0;
  --ink-faint: #a7aaa1;
  --line: #35382f;
  --line-strong: #505448;
  --math: #8fa8ff;
  --math-soft: #222d54;
  --physics: #ef9a79;
  --physics-soft: #4c2c22;
  --signal: #c9f24d;
  --success: #63d39b;
  --error: #ff958c;
  --shadow: 0 20px 60px rgba(0, 0, 0, 0.28);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  min-width: 320px;
  background: var(--paper);
  color: var(--ink);
  font-family: var(--sans);
  font-size: 16px;
  line-height: 1.65;
  text-rendering: optimizeLegibility;
}
button, input { font: inherit; }
button, a { -webkit-tap-highlight-color: transparent; }
a { color: inherit; }
svg { display: block; }

.skip-link {
  position: fixed;
  left: 12px;
  top: -60px;
  z-index: 1000;
  padding: 10px 14px;
  border-radius: var(--radius-sm);
  background: var(--ink);
  color: var(--paper);
  text-decoration: none;
  border: 0;
  transition: top .18s ease;
}
.skip-link:focus { top: 10px; }

:focus-visible {
  outline: 3px solid color-mix(in srgb, var(--math) 72%, transparent);
  outline-offset: 3px;
}
h1[tabindex="-1"]:focus { outline: none; }

.topbar {
  position: fixed;
  inset: 0 0 auto 0;
  z-index: 50;
  height: var(--topbar-height);
  display: grid;
  grid-template-columns: var(--sidebar-width) 1fr auto;
  align-items: center;
  border-bottom: 1px solid var(--line);
  background: color-mix(in srgb, var(--paper) 90%, transparent);
  backdrop-filter: blur(18px);
}

.wordmark {
  height: 100%;
  display: flex;
  align-items: center;
  gap: 11px;
  padding: 0 22px;
  border-right: 1px solid var(--line);
  text-decoration: none;
}
.wordmark-mark {
  width: 34px;
  height: 34px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  background: var(--ink);
  color: var(--paper);
  font-family: var(--mono);
  font-size: 11px;
  letter-spacing: -.04em;
}
.wordmark strong, .wordmark small { display: block; }
.wordmark strong { font-size: 14px; line-height: 1.2; letter-spacing: -.015em; }
.wordmark small { margin-top: 2px; color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; letter-spacing: .06em; }
.topbar-context {
  display: flex;
  align-items: center;
  gap: 9px;
  padding: 0 24px;
  color: var(--ink-soft);
  font-size: 13px;
}
.status-dot { width: 7px; height: 7px; border-radius: 50%; background: var(--signal); box-shadow: 0 0 0 4px color-mix(in srgb, var(--signal) 22%, transparent); }
.topbar-actions { display: flex; gap: 8px; padding-right: 18px; }
.icon-button {
  width: 40px;
  height: 40px;
  display: grid;
  place-items: center;
  padding: 0;
  border: 1px solid var(--line);
  border-radius: 50%;
  background: var(--paper-raised);
  color: var(--ink);
  cursor: pointer;
  transition: border-color .18s ease, transform .18s ease, background .18s ease;
}
.icon-button:hover { border-color: var(--line-strong); transform: translateY(-1px); }
.icon-button svg { width: 18px; height: 18px; fill: none; stroke: currentColor; stroke-width: 1.7; stroke-linecap: round; stroke-linejoin: round; }
.moon-icon { display: none; }
[data-theme="dark"] .sun-icon { display: none; }
[data-theme="dark"] .moon-icon { display: block; }
.menu-button { display: none; }

.app-shell { min-height: 100vh; padding-top: var(--topbar-height); }
.sidebar {
  position: fixed;
  inset: var(--topbar-height) auto 0 0;
  z-index: 40;
  width: var(--sidebar-width);
  display: flex;
  flex-direction: column;
  padding: 24px 18px 18px;
  border-right: 1px solid var(--line);
  background: var(--paper);
}
.primary-nav { display: grid; gap: 5px; }
.primary-nav a {
  min-height: 44px;
  display: flex;
  align-items: center;
  gap: 11px;
  padding: 10px 12px;
  border-radius: 10px;
  color: var(--ink-soft);
  font-size: 13px;
  font-weight: 600;
  text-decoration: none;
  transition: background .16s ease, color .16s ease;
}
.primary-nav a:hover { color: var(--ink); background: var(--paper-deep); }
.primary-nav a.active { color: var(--ink); background: var(--paper-raised); box-shadow: inset 0 0 0 1px var(--line); }
.primary-nav svg { width: 18px; height: 18px; fill: none; stroke: currentColor; stroke-width: 1.7; stroke-linejoin: round; }
.nav-index { width: 18px; font-family: var(--mono); font-size: 10px; color: var(--ink-faint); }
.sidebar-progress { margin-top: 36px; padding: 16px 12px; border-top: 1px solid var(--line); border-bottom: 1px solid var(--line); }
.sidebar-progress-head { display: flex; justify-content: space-between; gap: 12px; font-family: var(--mono); font-size: 10px; text-transform: uppercase; letter-spacing: .06em; }
.sidebar-progress-head strong { color: var(--ink); }
.progress-track { height: 5px; margin: 13px 0 11px; overflow: hidden; border-radius: 999px; background: var(--paper-deep); }
.progress-track span { display: block; width: 0; height: 100%; border-radius: inherit; background: var(--ink); transition: width .35s ease; }
.sidebar-progress p, .sidebar-foot p { margin: 0; color: var(--ink-soft); font-size: 11px; line-height: 1.55; }
.sidebar-foot { margin-top: auto; padding: 16px 12px 4px; }
.workspace-links { display: grid; gap: 5px; margin: 13px 0 10px; }
.workspace-links a { color: var(--ink-soft); font-size: 10px; font-weight: 600; text-decoration: none; }
.workspace-links a:hover { color: var(--ink); }
.text-button { margin-top: 10px; padding: 0; border: 0; background: none; color: var(--ink); font-size: 11px; font-weight: 700; text-decoration: underline; text-underline-offset: 3px; cursor: pointer; }

main { min-height: calc(100vh - var(--topbar-height)); margin-left: var(--sidebar-width); }
.view { width: min(100%, 1500px); margin: 0 auto; padding: clamp(28px, 4vw, 64px); animation: view-in .28s ease both; }
@keyframes view-in { from { opacity: 0; transform: translateY(5px); } }
.eyebrow { display: block; margin-bottom: 10px; color: var(--ink-soft); font-family: var(--mono); font-size: 10px; font-weight: 500; text-transform: uppercase; letter-spacing: .11em; }
.display-title { margin: 0; font-family: var(--display); font-size: clamp(42px, 6.2vw, 84px); font-weight: 500; line-height: .96; letter-spacing: -.045em; }
.display-title em { font-weight: 500; color: var(--math); }
.lede { max-width: 660px; margin: 24px 0 0; color: var(--ink-soft); font-size: clamp(16px, 1.5vw, 20px); line-height: 1.65; }

.home-hero {
  position: relative;
  min-height: 430px;
  display: grid;
  grid-template-columns: minmax(0, 1.05fr) minmax(360px, .95fr);
  gap: clamp(32px, 7vw, 110px);
  align-items: center;
  padding: clamp(30px, 5vw, 80px) 0 clamp(50px, 7vw, 95px);
  border-bottom: 1px solid var(--line);
}
.hero-copy { position: relative; z-index: 2; }
.hero-actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 30px; }
.button {
  min-height: 44px;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 8px;
  padding: 10px 17px;
  border: 1px solid var(--ink);
  border-radius: 999px;
  background: var(--ink);
  color: var(--paper);
  font-size: 12px;
  font-weight: 700;
  text-decoration: none;
  cursor: pointer;
  transition: transform .18s ease, box-shadow .18s ease;
}
.button:hover { transform: translateY(-1px); box-shadow: 0 8px 20px rgba(0,0,0,.12); }
.button.secondary { background: transparent; color: var(--ink); border-color: var(--line-strong); }
.button.small { min-height: 36px; padding: 7px 13px; font-size: 11px; }
.hero-visual { position: relative; min-height: 300px; display: grid; place-items: center; }
.hero-visual::before { content: ""; position: absolute; width: min(390px, 90%); aspect-ratio: 1; border: 1px solid var(--line); border-radius: 50%; }
.hero-visual svg { position: relative; z-index: 1; width: min(500px, 100%); overflow: visible; }
.hero-visual .axis { stroke: var(--line-strong); stroke-width: 1; }
.hero-visual .curve-main { fill: none; stroke: var(--math); stroke-width: 3.2; stroke-linecap: round; }
.hero-visual .curve-secondary { fill: none; stroke: var(--physics); stroke-width: 2.1; stroke-dasharray: 5 7; }
.hero-visual circle { fill: var(--signal); stroke: var(--ink); stroke-width: 1.4; }
.hero-caption { position: absolute; right: 0; bottom: 6px; max-width: 190px; color: var(--ink-soft); font-family: var(--mono); font-size: 9px; line-height: 1.6; }

.home-stats { display: grid; grid-template-columns: repeat(4, 1fr); border-bottom: 1px solid var(--line); }
.stat { padding: 20px 18px; border-right: 1px solid var(--line); }
.stat:last-child { border-right: 0; }
.stat strong { display: block; font-family: var(--display); font-size: 28px; font-weight: 500; line-height: 1; }
.stat span { display: block; margin-top: 6px; color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; letter-spacing: .07em; }

.section-block { padding: clamp(48px, 7vw, 92px) 0; }
.section-head { display: flex; align-items: end; justify-content: space-between; gap: 28px; margin-bottom: 30px; }
.section-head h2 { max-width: 680px; margin: 0; font-family: var(--display); font-size: clamp(32px, 4vw, 52px); font-weight: 500; line-height: 1.02; letter-spacing: -.035em; }
.section-head p { max-width: 440px; margin: 0; color: var(--ink-soft); font-size: 13px; }

.track-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 18px; }
.track-card {
  position: relative;
  min-height: 320px;
  display: flex;
  flex-direction: column;
  padding: 28px;
  overflow: hidden;
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  background: var(--paper-raised);
  text-decoration: none;
  box-shadow: 0 1px 0 rgba(255,255,255,.3) inset;
  transition: transform .2s ease, border-color .2s ease, box-shadow .2s ease;
}
.track-card:hover { transform: translateY(-3px); border-color: var(--line-strong); box-shadow: var(--shadow); }
.track-card.math { --track-color: var(--math); --track-soft: var(--math-soft); }
.track-card.physics { --track-color: var(--physics); --track-soft: var(--physics-soft); }
.track-number { font-family: var(--mono); font-size: 10px; color: var(--track-color); letter-spacing: .08em; }
.track-card h3 { max-width: 420px; margin: 52px 0 14px; font-family: var(--display); font-size: clamp(32px, 3.5vw, 48px); font-weight: 500; line-height: 1; letter-spacing: -.035em; }
.track-card p { max-width: 470px; margin: 0; color: var(--ink-soft); font-size: 13px; }
.track-meta { display: flex; align-items: center; justify-content: space-between; gap: 16px; margin-top: auto; padding-top: 28px; font-family: var(--mono); font-size: 9px; text-transform: uppercase; letter-spacing: .06em; }
.track-arrow { width: 36px; height: 36px; display: grid; place-items: center; border-radius: 50%; background: var(--track-soft); color: var(--track-color); font-size: 18px; }

.recent-list { display: grid; border-top: 1px solid var(--line); }
.recent-item { display: grid; grid-template-columns: 70px 1fr auto; gap: 22px; align-items: center; padding: 18px 4px; border-bottom: 1px solid var(--line); text-decoration: none; }
.recent-item:hover .recent-title { color: var(--math); }
.recent-index { font-family: var(--mono); font-size: 10px; color: var(--ink-faint); }
.recent-title { font-weight: 700; transition: color .18s ease; }
.recent-subtitle { display: block; margin-top: 3px; color: var(--ink-soft); font-size: 11px; }
.recent-status { padding: 5px 8px; border: 1px solid var(--line); border-radius: 999px; font-family: var(--mono); font-size: 8px; text-transform: uppercase; letter-spacing: .05em; }
.recent-status.done { background: var(--signal); border-color: var(--signal); color: #141a08; }

.subject-hero { display: grid; grid-template-columns: minmax(0, 1.2fr) minmax(260px, .8fr); gap: 50px; align-items: end; padding-bottom: 48px; border-bottom: 1px solid var(--line); }
.subject-hero.math { --subject: var(--math); }
.subject-hero.physics { --subject: var(--physics); }
.subject-hero .display-title em { color: var(--subject); }
.subject-note { padding: 20px; border-left: 2px solid var(--subject); background: var(--paper-raised); color: var(--ink-soft); font-size: 12px; }
.subject-note strong { display: block; margin-bottom: 5px; color: var(--ink); }
.lesson-list { display: grid; margin-top: 42px; border-top: 1px solid var(--line); }
.lesson-row { display: grid; grid-template-columns: 64px minmax(0, 1fr) 120px 42px; gap: 22px; align-items: center; padding: 24px 4px; border-bottom: 1px solid var(--line); text-decoration: none; }
.lesson-row:hover .lesson-row-title { color: var(--subject-color, var(--math)); }
.lesson-row-index { font-family: var(--mono); font-size: 10px; color: var(--ink-faint); }
.lesson-row-title { font-family: var(--display); font-size: 24px; font-weight: 500; line-height: 1.1; transition: color .18s ease; }
.lesson-row-summary { display: block; max-width: 720px; margin-top: 6px; color: var(--ink-soft); font-family: var(--sans); font-size: 11px; line-height: 1.5; }
.lesson-row-meta { color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; line-height: 1.6; }
.lesson-row-action { width: 36px; height: 36px; display: grid; place-items: center; border: 1px solid var(--line); border-radius: 50%; }

.lesson-view { max-width: 1240px; }
.lesson-topline { display: flex; align-items: center; justify-content: space-between; gap: 20px; margin-bottom: 36px; }
.back-link { display: inline-flex; align-items: center; gap: 8px; color: var(--ink-soft); font-size: 11px; font-weight: 700; text-decoration: none; }
.back-link:hover { color: var(--ink); }
.lesson-progress-label { color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; letter-spacing: .07em; }
.lesson-header { display: grid; grid-template-columns: minmax(0, 1.15fr) minmax(300px, .85fr); gap: 56px; align-items: center; padding-bottom: 52px; border-bottom: 1px solid var(--line); }
.lesson-header.math { --lesson-accent: var(--math); --lesson-soft: var(--math-soft); }
.lesson-header.physics { --lesson-accent: var(--physics); --lesson-soft: var(--physics-soft); }
.lesson-kicker { color: var(--lesson-accent); font-family: var(--mono); font-size: 10px; font-weight: 500; text-transform: uppercase; letter-spacing: .09em; }
.lesson-title { max-width: 760px; margin: 14px 0 0; font-family: var(--display); font-size: clamp(42px, 5.3vw, 72px); font-weight: 500; line-height: .96; letter-spacing: -.045em; }
.lesson-summary { max-width: 680px; margin: 22px 0 0; color: var(--ink-soft); font-size: 15px; }
.lesson-facts { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 24px; }
.fact-pill { padding: 6px 9px; border: 1px solid var(--line); border-radius: 999px; color: var(--ink-soft); font-family: var(--mono); font-size: 8px; text-transform: uppercase; letter-spacing: .05em; }
.lesson-diagram { min-height: 300px; display: grid; place-items: center; padding: 22px; border-radius: var(--radius-lg); background: var(--lesson-soft); }
.lesson-diagram svg { width: 100%; max-height: 300px; }
.diagram-axis { stroke: color-mix(in srgb, var(--ink) 28%, transparent); stroke-width: 1; }
.diagram-grid { stroke: color-mix(in srgb, var(--ink) 10%, transparent); stroke-width: .7; }
.diagram-main { fill: none; stroke: var(--lesson-accent); stroke-width: 3; stroke-linecap: round; stroke-linejoin: round; }
.diagram-alt { fill: none; stroke: var(--ink); stroke-width: 1.8; stroke-dasharray: 5 5; opacity: .6; }
.diagram-point { fill: var(--signal); stroke: var(--ink); stroke-width: 1.2; }
.diagram-label { fill: var(--ink); font-family: var(--mono); font-size: 8px; }

.lesson-layout { display: grid; grid-template-columns: minmax(0, 1fr) 210px; gap: clamp(38px, 6vw, 82px); align-items: start; padding-top: 52px; }
.lesson-article { min-width: 0; max-width: 780px; }
.lesson-toc { position: sticky; top: calc(var(--topbar-height) + 28px); padding-left: 18px; border-left: 1px solid var(--line); }
.lesson-toc strong { display: block; margin-bottom: 12px; font-family: var(--mono); font-size: 9px; text-transform: uppercase; letter-spacing: .08em; }
.lesson-toc a, .lesson-toc button { display: block; padding: 5px 0; border: 0; background: none; color: var(--ink-soft); font-size: 10px; text-align: left; text-decoration: none; cursor: pointer; }
.lesson-toc a:hover, .lesson-toc button:hover { color: var(--ink); }
.content-section { scroll-margin-top: calc(var(--topbar-height) + 24px); padding-bottom: 54px; }
.content-section + .content-section { padding-top: 54px; border-top: 1px solid var(--line); }
.content-section h2 { margin: 0 0 22px; font-family: var(--display); font-size: clamp(30px, 3.5vw, 44px); font-weight: 500; line-height: 1.02; letter-spacing: -.03em; }
.content-section h3 { margin: 28px 0 10px; font-size: 14px; }
.content-section p { margin: 0 0 16px; color: var(--ink-soft); }
.content-section p strong { color: var(--ink); }
.content-section ul { margin: 16px 0 0; padding-left: 20px; color: var(--ink-soft); }
.content-section li + li { margin-top: 8px; }
.math-block { margin: 22px 0; padding: 18px 20px; overflow-x: auto; border-left: 3px solid var(--lesson-accent, var(--math)); background: var(--paper-raised); color: var(--ink); }
.margin-note { margin: 26px 0; padding: 18px 20px; border: 1px solid var(--line); border-radius: var(--radius-md); background: var(--paper-raised); }
.margin-note .note-label { display: block; margin-bottom: 7px; color: var(--lesson-accent, var(--math)); font-family: var(--mono); font-size: 9px; font-weight: 500; text-transform: uppercase; letter-spacing: .08em; }
.margin-note p:last-child { margin-bottom: 0; }

.example-list { display: grid; gap: 14px; }
.example-card { overflow: hidden; border: 1px solid var(--line); border-radius: var(--radius-md); background: var(--paper-raised); }
.example-head { width: 100%; display: grid; grid-template-columns: 42px 1fr auto; gap: 12px; align-items: center; padding: 16px; border: 0; background: transparent; color: var(--ink); text-align: left; cursor: pointer; }
.example-number { width: 34px; height: 34px; display: grid; place-items: center; border-radius: 50%; background: var(--lesson-soft, var(--math-soft)); color: var(--lesson-accent, var(--math)); font-family: var(--mono); font-size: 9px; }
.example-head strong { font-size: 12px; }
.example-head span:last-child { color: var(--ink-faint); font-size: 18px; transition: transform .2s ease; }
.example-card.open .example-head span:last-child { transform: rotate(45deg); }
.example-body { display: none; padding: 0 20px 20px 70px; }
.example-card.open .example-body { display: block; animation: reveal .22s ease both; }
@keyframes reveal { from { opacity: 0; transform: translateY(-4px); } }
.example-prompt { margin: 0 0 18px; color: var(--ink); }
.solution-steps { margin: 0; padding: 0; list-style: none; counter-reset: steps; }
.solution-steps li { position: relative; min-height: 30px; padding-left: 28px; color: var(--ink-soft); font-size: 12px; }
.solution-steps li::before { counter-increment: steps; content: counter(steps); position: absolute; left: 0; top: 1px; width: 18px; height: 18px; display: grid; place-items: center; border: 1px solid var(--line-strong); border-radius: 50%; color: var(--ink); font-family: var(--mono); font-size: 8px; }
.example-answer { margin-top: 16px; padding-top: 14px; border-top: 1px solid var(--line); color: var(--ink); font-weight: 700; }

.practice-intro { display: flex; align-items: end; justify-content: space-between; gap: 20px; margin-bottom: 22px; }
.practice-intro p { max-width: 520px; margin: 0; }
.practice-score { color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.problem-list { display: grid; gap: 18px; }
.problem-card { padding: 22px; border: 1px solid var(--line); border-radius: var(--radius-md); background: var(--paper-raised); }
.problem-meta { display: flex; align-items: center; justify-content: space-between; gap: 12px; margin-bottom: 14px; color: var(--ink-faint); font-family: var(--mono); font-size: 8px; text-transform: uppercase; letter-spacing: .06em; }
.problem-prompt { margin: 0 0 18px; color: var(--ink); font-size: 14px; }
.choice-list { display: grid; gap: 8px; }
.choice { position: relative; }
.choice input { position: absolute; opacity: 0; pointer-events: none; }
.choice label { display: grid; grid-template-columns: 26px 1fr; gap: 10px; align-items: center; min-height: 44px; padding: 9px 12px; border: 1px solid var(--line); border-radius: 10px; color: var(--ink-soft); font-size: 12px; cursor: pointer; transition: border-color .16s ease, background .16s ease, color .16s ease; }
.choice label::before { content: attr(data-letter); width: 24px; height: 24px; display: grid; place-items: center; border: 1px solid var(--line); border-radius: 50%; font-family: var(--mono); font-size: 8px; }
.choice input:checked + label { border-color: var(--ink); color: var(--ink); background: var(--paper-deep); }
.choice.correct label { border-color: var(--success); color: var(--success); }
.choice.incorrect label { border-color: var(--error); color: var(--error); }
.problem-actions { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 16px; }
.feedback { display: none; margin-top: 16px; padding: 14px 16px; border-radius: 10px; font-size: 11px; }
.feedback.visible { display: block; animation: reveal .2s ease both; }
.feedback.correct { background: color-mix(in srgb, var(--success) 12%, transparent); color: var(--success); }
.feedback.incorrect { background: color-mix(in srgb, var(--error) 10%, transparent); color: var(--error); }
.hint { display: none; margin: 12px 0 0; color: var(--ink-soft); font-size: 11px; }
.hint.visible { display: block; }
.lesson-complete { margin-top: 54px; padding: 24px; border-radius: var(--radius-lg); background: var(--ink); color: var(--paper); }
.lesson-complete h3 { margin: 0 0 7px; font-family: var(--display); font-size: 28px; font-weight: 500; }
.lesson-complete p { margin: 0 0 18px; color: color-mix(in srgb, var(--paper) 72%, transparent); font-size: 12px; }
.lesson-complete .button { background: var(--signal); border-color: var(--signal); color: #11170a; }

.resource-grid { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 12px; margin-top: 30px; }
.resource-card { padding: 16px; border: 1px solid var(--line); border-radius: var(--radius-md); text-decoration: none; }
.resource-card:hover { background: var(--paper-raised); }
.resource-card strong { display: block; font-size: 12px; }
.resource-card span { display: block; margin-top: 5px; color: var(--ink-soft); font-family: var(--mono); font-size: 8px; text-transform: uppercase; }

.drawer-scrim { position: fixed; inset: 0; z-index: 80; background: rgba(15, 16, 13, .4); backdrop-filter: blur(2px); }
.reference-drawer { position: fixed; inset: 0 0 0 auto; z-index: 90; width: min(460px, 100%); padding: 26px; overflow-y: auto; border-left: 1px solid var(--line); background: var(--paper-raised); box-shadow: var(--shadow); transform: translateX(102%); visibility: hidden; transition: transform .28s cubic-bezier(.22,.8,.24,1), visibility 0s linear .28s; }
.reference-drawer.open { transform: translateX(0); visibility: visible; transition: transform .28s cubic-bezier(.22,.8,.24,1), visibility 0s linear 0s; }
.has-overlay { overflow: hidden; }
.drawer-head { display: flex; align-items: start; justify-content: space-between; gap: 20px; padding-bottom: 22px; border-bottom: 1px solid var(--line); }
.drawer-head h2 { margin: 0; font-family: var(--display); font-size: 36px; font-weight: 500; }
.reference-tabs { display: grid; grid-template-columns: 1fr 1fr; gap: 4px; margin: 20px 0; padding: 4px; border-radius: 999px; background: var(--paper-deep); }
.reference-tabs button { padding: 9px; border: 0; border-radius: 999px; background: transparent; color: var(--ink-soft); font-size: 11px; cursor: pointer; }
.reference-tabs button[aria-selected="true"] { background: var(--paper-raised); color: var(--ink); box-shadow: 0 1px 4px rgba(0,0,0,.08); }
.reference-group { padding: 20px 0; border-bottom: 1px solid var(--line); }
.reference-group h3 { margin: 0 0 12px; font-size: 12px; }
.reference-formula { margin: 8px 0; padding: 12px; overflow-x: auto; border-radius: 8px; background: var(--paper); font-size: 12px; }
.reference-group p { margin: 8px 0 0; color: var(--ink-soft); font-size: 11px; }

.empty-state { max-width: 640px; padding: 80px 0; }
.empty-state h1 { margin: 0; font-family: var(--display); font-size: 56px; font-weight: 500; }
.empty-state p { color: var(--ink-soft); }
.toast { position: fixed; left: 50%; bottom: 24px; z-index: 120; max-width: calc(100% - 32px); padding: 10px 14px; border-radius: 999px; background: var(--ink); color: var(--paper); font-size: 11px; box-shadow: var(--shadow); opacity: 0; transform: translate(-50%, 12px); pointer-events: none; transition: opacity .2s ease, transform .2s ease; }
.toast.visible { opacity: 1; transform: translate(-50%, 0); }

@media (max-width: 1050px) {
  :root { --sidebar-width: 210px; }
  .home-hero, .lesson-header { grid-template-columns: 1fr; }
  .hero-visual { max-width: 650px; width: 100%; justify-self: center; }
  .lesson-diagram { min-height: 250px; }
  .lesson-layout { grid-template-columns: 1fr; }
  .lesson-toc { position: static; order: -1; display: flex; flex-wrap: wrap; gap: 8px 14px; padding: 0 0 18px; border-left: 0; border-bottom: 1px solid var(--line); }
  .lesson-toc strong { width: 100%; margin-bottom: 0; }
}

@media (max-width: 780px) {
  :root { --topbar-height: 64px; }
  .topbar { grid-template-columns: 1fr auto; }
  .wordmark { border-right: 0; padding-left: 14px; }
  .topbar-context { display: none; }
  .topbar-actions { padding-right: 12px; }
  .menu-button { display: grid; }
  .sidebar { width: min(310px, 88vw); transform: translateX(-102%); transition: transform .25s ease; box-shadow: var(--shadow); }
  .sidebar.open { transform: translateX(0); }
  main { margin-left: 0; }
  .view { padding: 28px 18px 56px; }
  .home-hero { min-height: 0; grid-template-columns: 1fr; padding-top: 24px; }
  .hero-visual { min-height: 250px; }
  .hero-caption { display: none; }
  .home-stats { grid-template-columns: 1fr 1fr; }
  .stat:nth-child(2) { border-right: 0; }
  .stat:nth-child(-n+2) { border-bottom: 1px solid var(--line); }
  .track-grid { grid-template-columns: 1fr; }
  .section-head, .subject-hero { display: block; }
  .section-head p, .subject-note { margin-top: 18px; }
  .lesson-row { grid-template-columns: 38px 1fr 36px; gap: 12px; }
  .lesson-row-meta { display: none; }
  .recent-item { grid-template-columns: 40px 1fr; }
  .recent-status { display: none; }
  .lesson-header { gap: 34px; }
  .lesson-diagram { min-height: 220px; }
  .example-body { padding-left: 20px; }
  .resource-grid { grid-template-columns: 1fr; }
}

@media (max-width: 470px) {
  .wordmark small { display: none; }
  .topbar-actions { gap: 5px; }
  .icon-button { width: 36px; height: 36px; }
  .display-title { font-size: 48px; }
  .lesson-title { font-size: 45px; }
  .home-stats { grid-template-columns: 1fr; }
  .stat { border-right: 0; border-bottom: 1px solid var(--line); }
  .stat:last-child { border-bottom: 0; }
  .track-card { min-height: 290px; padding: 22px; }
  .lesson-topline { align-items: flex-start; }
  .practice-intro { display: block; }
  .practice-score { margin-top: 10px; }
}

@media (prefers-reduced-motion: reduce) {
  *, *::before, *::after { scroll-behavior: auto !important; animation-duration: .01ms !important; transition-duration: .01ms !important; }
}

/* Application composition */
.sr-only { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0, 0, 0, 0); white-space: nowrap; border: 0; }
.page-shell { width: 100%; }
.hero-copy h1, .subject-header h1, .lesson-hero h1 { margin: 0; font-family: var(--display); font-weight: 500; line-height: .96; letter-spacing: -.045em; }
.hero-copy h1 { max-width: 760px; font-size: clamp(46px, 6.2vw, 84px); }
.hero-copy h1 em { color: var(--math); font-weight: inherit; }
.hero-lede { max-width: 670px; margin: 24px 0 0; color: var(--ink-soft); font-size: clamp(16px, 1.5vw, 20px); }
.button-quiet { background: transparent; color: var(--ink); border-color: var(--line-strong); }
.button-small { min-height: 36px; padding: 7px 13px; font-size: 11px; }
.overview-section { padding: clamp(48px, 7vw, 92px) 0; }
.section-heading { display: flex; align-items: end; justify-content: space-between; gap: 28px; margin-bottom: 30px; }
.section-heading h2, .progress-panel h2, .resource-section h2 { margin: 0; font-family: var(--display); font-size: clamp(32px, 4vw, 52px); font-weight: 500; line-height: 1.02; letter-spacing: -.035em; }
.section-heading > p { max-width: 440px; margin: 0; color: var(--ink-soft); font-size: 13px; }
.section-heading.compact { margin-bottom: 18px; }
.track-card-top { display: flex; align-items: center; justify-content: space-between; }
.track-status, .track-code { color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; letter-spacing: .07em; }
.track-code { margin: 48px 0 0 !important; color: var(--track-color) !important; }
.track-card h3 { margin-top: 10px; }
.track-focus { display: flex; justify-content: space-between; gap: 18px; margin-top: auto; padding-top: 24px; color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.track-focus strong { color: var(--ink); font-weight: 500; text-align: right; }
.text-link { margin-top: 18px; color: var(--track-color); font-size: 12px; font-weight: 700; text-decoration: none; }
.progress-panel { display: grid; grid-template-columns: 1fr 1.4fr; gap: 40px; align-items: end; padding: clamp(38px, 5vw, 62px) 0; border-top: 1px solid var(--line); }
.stat-grid { display: grid; grid-template-columns: repeat(3, 1fr); }
.stat { border-left: 1px solid var(--line); border-right: 0; }
.stat strong span { display: inline; margin: 0; color: var(--ink-faint); font-size: .55em; }
.stat small { display: block; margin-top: 7px; color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; }

.subject-header { max-width: 1000px; padding: 14px 0 50px; }
.subject-header h1 { max-width: 920px; font-size: clamp(48px, 7vw, 88px); }
.subject-page.math .subject-header h1 { color: var(--math); }
.subject-page.physics .subject-header h1 { color: var(--physics); }
.subject-header > p:last-child { max-width: 720px; margin: 24px 0 0; color: var(--ink-soft); font-size: 16px; }
.lesson-index { padding: 48px 0; border-top: 1px solid var(--line); }
.lesson-row { grid-template-columns: 64px minmax(0,1fr) 155px auto 42px; }
.lesson-index-number { color: var(--ink-faint); font-family: var(--mono); font-size: 10px; }
.lesson-row-main strong { display: block; font-family: var(--display); font-size: 25px; font-weight: 500; line-height: 1.1; }
.lesson-row-main small, .lesson-meta { display: block; color: var(--ink-soft); font-size: 11px; }
.lesson-meta { font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.status-pill { padding: 5px 8px; border: 1px solid var(--line); border-radius: 999px; font-family: var(--mono); font-size: 8px; text-transform: uppercase; white-space: nowrap; }
.status-pill.complete { background: var(--signal); border-color: var(--signal); color: #141a08; }
.row-arrow { width: 36px; height: 36px; display: grid; place-items: center; border: 1px solid var(--line); border-radius: 50%; }
.scope-note { padding: 22px; border-left: 3px solid var(--math); background: var(--paper-raised); }
.physics .scope-note { border-color: var(--physics); }
.scope-note span { font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.scope-note p { margin: 6px 0 0; color: var(--ink-soft); font-size: 12px; }
.resource-section { padding: 56px 0 22px; }
.resource-card { display: grid; grid-template-columns: auto 1fr auto; gap: 14px; align-items: center; }
.resource-card span { margin: 0; }
.resource-card small { display: block; margin-top: 4px; color: var(--ink-soft); font-family: var(--mono); font-size: 8px; text-transform: uppercase; }
.pdf-mark { width: 38px; height: 38px; display: grid !important; place-items: center; border-radius: 50%; background: var(--paper-deep); color: var(--ink) !important; }

.lesson-hero { padding-bottom: 48px; border-bottom: 1px solid var(--line); }
.lesson-hero .back-link { margin-bottom: 38px; }
.lesson-kicker { display: flex; flex-wrap: wrap; gap: 10px; margin-bottom: 16px; color: var(--math); }
.lesson-kicker span { padding-right: 10px; border-right: 1px solid var(--line); }
.lesson-kicker span:last-child { border: 0; }
.lesson-page.physics .lesson-kicker { color: var(--physics); }
.lesson-hero h1 { max-width: 970px; font-size: clamp(48px, 6.3vw, 80px); }
.lesson-subtitle { margin: 12px 0 0; color: var(--math); font-family: var(--display); font-size: 26px; }
.lesson-page.physics .lesson-subtitle { color: var(--physics); }
.lesson-summary { max-width: 720px; }
.skill-list { display: flex; flex-wrap: wrap; gap: 8px; margin-top: 24px; }
.skill-list span { padding: 6px 9px; border: 1px solid var(--line); border-radius: 999px; color: var(--ink-soft); font-family: var(--mono); font-size: 8px; text-transform: uppercase; }
.lesson-layout { grid-template-columns: 190px minmax(0, 1fr); }
.lesson-reader { min-width: 0; max-width: 900px; }
.lesson-figure { min-height: 300px; display: grid; place-items: center; margin-bottom: 58px; padding: 24px; border-radius: var(--radius-lg); background: var(--math-soft); }
.lesson-page.physics .lesson-figure { background: var(--physics-soft); }
.lesson-figure svg { width: 100%; max-height: 300px; }
.reader-section { scroll-margin-top: calc(var(--topbar-height) + 24px); padding-bottom: 54px; }
.reader-section + .reader-section { padding-top: 54px; border-top: 1px solid var(--line); }
.reader-section h2, .discussion-block h2 { margin: 0 0 22px; font-family: var(--display); font-size: clamp(30px, 3.5vw, 44px); font-weight: 500; line-height: 1.02; }
.reader-section p { color: var(--ink-soft); }
.discussion-block + .discussion-block { margin-top: 48px; padding-top: 42px; border-top: 1px dashed var(--line); }
.math-display { margin: 22px 0; padding: 18px 20px; overflow-x: auto; border-left: 3px solid var(--math); background: var(--paper-raised); }
.physics .math-display { border-color: var(--physics); }
.concept-note { margin: 26px 0; padding: 18px 20px; border: 1px solid var(--line); border-radius: var(--radius-md); background: var(--paper-raised); }
.concept-note span { color: var(--math); font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.physics .concept-note span { color: var(--physics); }
.concept-note p { margin: 7px 0 0; }
.section-intro { margin: -8px 0 22px; }
.example-toggle { width: 100%; display: grid; grid-template-columns: 1fr auto; gap: 12px; align-items: center; padding: 18px 20px; border: 0; background: transparent; color: var(--ink); text-align: left; cursor: pointer; }
.example-toggle small, .example-toggle strong { display: block; }
.example-toggle small { color: var(--ink-faint); font-family: var(--mono); font-size: 8px; text-transform: uppercase; }
.example-toggle strong { margin-top: 3px; font-size: 13px; }
.example-toggle .plus { font-size: 22px; transition: transform .2s ease; }
.example-toggle[aria-expanded="true"] .plus { transform: rotate(45deg); }
.example-body { display: block; padding: 0 20px 20px; }
.example-body[hidden] { display: none; }
.example-body ol { padding-left: 22px; color: var(--ink-soft); font-size: 12px; }
.example-body li + li { margin-top: 8px; }
.example-answer span { color: var(--math); font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.physics .example-answer span { color: var(--physics); }
.example-answer p { margin: 4px 0 0; color: var(--ink); }
.practice-heading { display: flex; align-items: end; justify-content: space-between; gap: 20px; margin-bottom: 24px; }
.lesson-score { text-align: right; }
.lesson-score strong, .lesson-score span { display: block; }
.lesson-score strong { font-family: var(--display); font-size: 30px; font-weight: 500; }
.lesson-score span { color: var(--ink-soft); font-family: var(--mono); font-size: 8px; text-transform: uppercase; }
.problem-top { display: flex; justify-content: space-between; margin-bottom: 14px; color: var(--ink-faint); font-family: var(--mono); font-size: 8px; text-transform: uppercase; }
.problem-top div { display: flex; gap: 8px; }
.problem-card fieldset { display: grid; gap: 8px; margin: 0; padding: 0; border: 0; }
.problem-card .choice { display: grid; grid-template-columns: 26px 1fr; gap: 10px; align-items: center; min-height: 44px; padding: 9px 12px; border: 1px solid var(--line); border-radius: 10px; color: var(--ink-soft); font-size: 12px; cursor: pointer; }
.problem-card .choice:has(input:checked) { border-color: var(--ink); color: var(--ink); background: var(--paper-deep); }
.problem-card .choice:has(input:focus-visible) { outline: 3px solid color-mix(in srgb, var(--math) 72%, transparent); outline-offset: 3px; }
.problem-card .choice input { position: absolute; opacity: 0; }
.choice-letter { width: 24px; height: 24px; display: grid; place-items: center; border: 1px solid var(--line); border-radius: 50%; font-family: var(--mono); font-size: 8px; }
.problem-card.is-correct { border-color: var(--success); }
.problem-card.is-incorrect { border-color: var(--error); }
.problem-actions .text-button { margin: 0 0 0 5px; }
.hint-box, .feedback-box { margin-top: 14px; padding: 14px 16px; border-radius: 10px; background: var(--paper-deep); font-size: 11px; }
.hint-box[hidden], .feedback-box[hidden] { display: none; }
.hint-box strong, .feedback-box strong { color: var(--ink); }
.hint-box p, .feedback-box p { margin: 4px 0 0; }
.is-correct .feedback-box { background: color-mix(in srgb, var(--success) 12%, transparent); }
.is-incorrect .feedback-box { background: color-mix(in srgb, var(--error) 10%, transparent); }
.source-sets { margin-top: 56px; padding-top: 48px; border-top: 1px solid var(--line); }
.source-sets-head { display: flex; align-items: end; justify-content: space-between; gap: 24px; margin-bottom: 24px; }
.source-sets-head h3 { margin: 0; font-family: var(--display); font-size: 34px; font-weight: 500; }
.source-sets-head > p { max-width: 430px; margin: 0; font-size: 11px; }
.source-set { margin-top: 18px; overflow: hidden; border: 1px solid var(--line); border-radius: var(--radius-md); background: var(--paper-raised); }
.source-set > header { display: flex; align-items: end; justify-content: space-between; gap: 20px; padding: 18px 20px; border-bottom: 1px solid var(--line); }
.source-set > header span, .source-set > header small { color: var(--math); font-family: var(--mono); font-size: 8px; text-transform: uppercase; letter-spacing: .07em; }
.physics .source-set > header span, .physics .source-set > header small { color: var(--physics); }
.source-set > header h4 { margin: 3px 0 0; font-family: var(--display); font-size: 24px; font-weight: 500; }
.source-set > ol { margin: 0; padding: 0; list-style: none; }
.source-item { padding: 20px; }
.source-item + .source-item { border-top: 1px solid var(--line); }
.source-item-top { display: grid; grid-template-columns: 28px 1fr; gap: 12px; }
.source-item-top > span { color: var(--ink-faint); font-family: var(--mono); font-size: 9px; }
.source-item-top strong { font-size: 13px; font-weight: 600; }
.source-parts { margin: 12px 0 0 40px; padding-left: 18px; color: var(--ink-soft); font-size: 12px; }
.source-parts li + li { margin-top: 5px; }
.source-item > .text-button { margin: 14px 0 0 40px; }
.source-visual { margin: 16px 0 0 40px; padding: 12px; border: 1px solid var(--line); border-radius: 10px; background: var(--paper); }
.source-visual svg { width: 100%; max-height: 250px; }
.source-visual text { fill: var(--ink-soft); font-family: var(--mono); font-size: 10px; }
.source-answer .source-visual { margin-left: 0; background: var(--paper-raised); }
.source-answer { margin: 14px 0 0 40px; padding: 14px 16px; border-left: 3px solid var(--math); background: var(--paper-deep); }
.physics .source-answer { border-color: var(--physics); }
.source-answer[hidden] { display: none; }
.source-answer span { color: var(--math); font-family: var(--mono); font-size: 8px; text-transform: uppercase; }
.physics .source-answer span { color: var(--physics); }
.source-answer p { margin: 5px 0 0; color: var(--ink); font-size: 12px; }
.materials-section > p { max-width: 700px; }
.lesson-finish { display: flex; align-items: center; justify-content: space-between; gap: 24px; margin-top: 20px; padding: 24px; border-radius: var(--radius-lg); background: var(--ink); color: var(--paper); }
.lesson-finish span, .lesson-finish strong { display: block; }
.lesson-finish span { opacity: .7; font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.lesson-finish .button { background: var(--signal); border-color: var(--signal); color: #11170a; }

.lesson-figure .axis, .hero-svg .axis { fill: none; stroke: var(--line-strong); stroke-width: 1.2; }
.lesson-figure .curve, .hero-svg .curve { fill: none; stroke-width: 3; stroke-linecap: round; stroke-linejoin: round; }
.math-stroke { stroke: var(--math); fill: none; }
.physics-stroke, .motion-line { stroke: var(--physics); fill: none; stroke-width: 3; stroke-linecap: round; stroke-linejoin: round; }
.muted-stroke { stroke: var(--ink-faint); fill: none; }
.guide { stroke: var(--line-strong); stroke-width: 1; stroke-dasharray: 5 5; fill: none; }
.tangent, .map-arrow { stroke: var(--ink); stroke-width: 1.6; fill: none; }
.positive-area { fill: color-mix(in srgb, var(--physics) 22%, transparent); }
.negative-area { fill: color-mix(in srgb, var(--math) 18%, transparent); }
.panel-shape { fill: var(--paper-raised); stroke: var(--line-strong); }
.math-fill { fill: var(--math); }
.lesson-figure text, .hero-svg text { fill: var(--ink-soft); font-family: var(--mono); font-size: 12px; }
.hero-svg .motion-line { stroke-width: 2; stroke-dasharray: 6 6; }

/* Parent ledger */
.ledger-gate { min-height: calc(100vh - var(--topbar-height) - 128px); display: grid; grid-template-columns: minmax(0,1.15fr) minmax(340px,.65fr); gap: clamp(48px,9vw,140px); align-items: center; }
.ledger-gate-copy h1, .ledger-header h1 { margin: 0; font-family: var(--display); font-size: clamp(48px,6vw,82px); font-weight: 500; line-height: .96; letter-spacing: -.045em; }
.ledger-gate-copy h1 em { color: var(--physics); font-weight: inherit; }
.ledger-gate-copy > p { max-width: 650px; margin: 24px 0; color: var(--ink-soft); font-size: 16px; }
.ledger-gate-copy aside { max-width: 590px; display: grid; grid-template-columns: auto 1fr; gap: 16px; padding: 16px 0; border-top: 1px solid var(--line); color: var(--ink-soft); font-size: 11px; }
.ledger-gate-copy aside strong { color: var(--ink); }
.ledger-unlock { padding: 30px; border: 1px solid var(--line); border-radius: var(--radius-lg); background: var(--paper-raised); box-shadow: var(--shadow); }
.lock-mark { width: 44px; height: 44px; display: grid; place-items: center; border-radius: 50%; background: var(--ink); color: var(--paper); font-family: var(--mono); font-size: 10px; }
.ledger-unlock h2, .panel-heading h2, .ledger-history h2 { margin: 22px 0 4px; font-family: var(--display); font-size: 32px; font-weight: 500; }
.ledger-unlock > p { margin: 0 0 20px; color: var(--ink-soft); font-size: 12px; }
.role-switch { display: grid; grid-template-columns: 1fr 1fr; gap: 4px; margin-bottom: 18px; padding: 4px; border-radius: 999px; background: var(--paper-deep); }
.role-switch button { padding: 9px; border: 0; border-radius: 999px; background: transparent; color: var(--ink-soft); font-size: 11px; cursor: pointer; }
.role-switch button.active { background: var(--paper-raised); color: var(--ink); box-shadow: 0 1px 5px rgba(0,0,0,.08); }
.ledger-unlock label, .session-form-panel label { display: grid; gap: 6px; color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; letter-spacing: .06em; }
.ledger-unlock input, .session-form-panel input, .session-form-panel select, .session-form-panel textarea, #ledger-filter { width: 100%; min-height: 44px; padding: 10px 12px; border: 1px solid var(--line); border-radius: 9px; background: var(--paper); color: var(--ink); font-family: var(--sans); font-size: 12px; text-transform: none; }
.ledger-unlock .button { width: 100%; margin-top: 16px; }
.form-error { margin: 9px 0 0 !important; color: var(--error) !important; font-size: 11px !important; }
.form-error[hidden] { display: none; }
.ledger-loading { min-height: 60vh; display: grid; place-content: center; justify-items: center; gap: 18px; color: var(--ink-soft); }
.ledger-loading strong { font-family: var(--display); font-size: 28px; font-weight: 500; }
.ledger-page { padding-bottom: 40px; }
.ledger-header { display: flex; justify-content: space-between; gap: 36px; align-items: end; padding-bottom: 46px; border-bottom: 1px solid var(--line); }
.ledger-header h1 { font-size: clamp(46px,6vw,76px); }
.ledger-header > div:first-child > p:last-child { max-width: 650px; margin: 18px 0 0; color: var(--ink-soft); }
.ledger-header-actions { display: flex; align-items: center; gap: 14px; }
.ledger-header-actions .text-button { margin: 0; }
.ledger-sync { display: flex; align-items: center; gap: 9px; padding: 13px 0; border-bottom: 1px solid var(--line); color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.ledger-sync small { margin-left: auto; font: inherit; }
.ledger-notice { margin: 16px 0 0; padding: 12px 14px; border-left: 3px solid var(--physics); background: color-mix(in srgb, var(--physics) 8%, transparent); color: var(--ink-soft); font-size: 12px; }
.account-settings { margin-top: 14px; border: 1px solid var(--line); border-radius: var(--radius-md); background: var(--paper-raised); }
.account-settings summary { display: flex; justify-content: space-between; gap: 18px; padding: 14px 16px; cursor: pointer; list-style: none; }
.account-settings summary::-webkit-details-marker { display: none; }
.account-settings summary span { font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.account-settings summary small { color: var(--ink-soft); font-family: var(--mono); font-size: 9px; }
.account-settings-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 1px; border-top: 1px solid var(--line); background: var(--line); }
.account-settings form { display: grid; gap: 13px; padding: 20px; background: var(--paper-raised); }
.account-settings form > div strong { font-size: 12px; }
.account-settings form > div p { margin: 3px 0 0; color: var(--ink-soft); font-size: 10px; }
.account-settings label { display: grid; gap: 6px; color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.account-settings input { width: 100%; min-height: 42px; padding: 10px 12px; border: 1px solid var(--line); border-radius: 9px; background: var(--paper); color: var(--ink); font: 12px var(--sans); text-transform: none; }
.ledger-summary { display: grid; grid-template-columns: 1.3fr 1fr 1fr; border-bottom: 1px solid var(--line); }
.ledger-summary article { padding: 28px 24px; border-right: 1px solid var(--line); }
.ledger-summary article:last-child { border: 0; }
.ledger-summary span, .ledger-summary small { display: block; color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.ledger-summary strong { display: block; margin: 8px 0; font-family: var(--display); font-size: 36px; font-weight: 500; }
.ledger-columns { display: grid; grid-template-columns: 1fr 1fr; gap: 18px; padding: 54px 0; }
.payment-panel, .session-form-panel, .parent-note { padding: 26px; border: 1px solid var(--line); border-radius: var(--radius-lg); background: var(--paper-raised); }
.tutor-tools-stack { display: grid; gap: 18px; }
.panel-heading h2 { margin-top: 0; }
.payment-method-list { display: grid; grid-template-columns: 1fr 1fr; gap: 10px; margin-top: 24px; }
.payment-method-list article { padding: 18px; border: 1px solid var(--line); border-radius: var(--radius-md); background: var(--paper); }
.payment-method-list span { color: var(--physics); font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.payment-method-list strong { display: block; margin-top: 18px; font-family: var(--display); font-size: 23px; font-weight: 500; }
.payment-method-list p { margin: 2px 0 10px; color: var(--ink-soft); font-size: 11px; }
.payment-method-list .text-button { margin: 0; }
.pricing-strip { display: grid; grid-template-columns: auto 1fr; gap: 2px 14px; margin-top: 16px; padding: 15px 18px; border-left: 3px solid var(--signal); background: var(--paper-deep); }
.pricing-strip span { grid-row: span 2; color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.pricing-strip strong { font-size: 12px; }
.pricing-strip small { color: var(--ink-soft); font-size: 10px; }
.session-form-panel form { display: grid; grid-template-columns: 1fr 1fr; gap: 13px; margin-top: 24px; }
.session-form-panel .wide { grid-column: 1 / -1; }
.session-form-panel textarea { resize: vertical; }
.session-form-panel form > .button { align-self: end; }
.parent-note { align-self: start; border-left: 3px solid var(--physics); }
.parent-note span { font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.parent-note p { margin: 7px 0 0; color: var(--ink-soft); font-size: 12px; }
.ledger-history { padding-top: 50px; border-top: 1px solid var(--line); }
.ledger-history-head { display: flex; align-items: end; justify-content: space-between; gap: 20px; margin-bottom: 22px; }
.ledger-history h2 { margin: 0; font-size: 42px; }
.ledger-history-head label { display: grid; grid-template-columns: auto 150px; align-items: center; gap: 9px; color: var(--ink-soft); font-family: var(--mono); font-size: 9px; text-transform: uppercase; }
.session-list { border-top: 1px solid var(--line); }
.session-row { display: grid; grid-template-columns: 170px minmax(0,1fr) 140px auto; gap: 22px; align-items: center; padding: 19px 4px; border-bottom: 1px solid var(--line); }
.session-date strong, .session-date span, .session-topic span, .session-topic strong { display: block; }
.session-date strong, .session-topic strong { font-size: 12px; }
.session-date span, .session-topic span { color: var(--ink-soft); font-family: var(--mono); font-size: 8px; text-transform: uppercase; }
.session-topic p { margin: 4px 0 0; color: var(--ink-soft); font-size: 10px; }
.session-amount { text-align: right; }
.session-amount > strong { display: block; font-family: var(--display); font-size: 22px; font-weight: 500; }
.ledger-status { display: inline-block; margin-top: 4px; padding: 3px 7px; border-radius: 999px; font-family: var(--mono); font-size: 8px; text-transform: uppercase; }
.ledger-status.paid { background: color-mix(in srgb, var(--success) 13%, transparent); color: var(--success); }
.ledger-status.unpaid { background: color-mix(in srgb, var(--physics) 13%, transparent); color: var(--physics); }
.ledger-status.partial { background: color-mix(in srgb, #a86b13 14%, transparent); color: #8b590f; }
.session-actions { display: flex; gap: 6px; }
.session-actions button { padding: 7px 9px; border: 1px solid var(--line); border-radius: 999px; background: transparent; color: var(--ink); font-size: 9px; cursor: pointer; }
.ledger-empty { padding: 44px 4px; }
.ledger-empty strong { font-family: var(--display); font-size: 26px; font-weight: 500; }
.ledger-empty p { margin: 5px 0; color: var(--ink-soft); font-size: 12px; }
.payment-history { margin-top: 64px; }
.entry-list { border-top: 1px solid var(--line); }
.entry-row { display: grid; grid-template-columns: minmax(0,1fr) 150px auto; gap: 20px; align-items: center; padding: 18px 4px; border-bottom: 1px solid var(--line); }
.entry-row > div span, .entry-row > div strong { display: block; }
.entry-row > div span { color: var(--ink-soft); font-family: var(--mono); font-size: 8px; text-transform: uppercase; }
.entry-row > div strong { margin-top: 3px; font-size: 12px; }
.entry-row > div p { margin: 4px 0 0; color: var(--ink-soft); font-size: 10px; }
.entry-row > strong { font-family: var(--display); font-size: 22px; font-weight: 500; text-align: right; }
.entry-row > button { padding: 7px 9px; border: 1px solid var(--line); border-radius: 999px; background: transparent; color: var(--ink); font-size: 9px; cursor: pointer; }

@media (max-width: 1050px) {
  .lesson-layout { grid-template-columns: 1fr; }
  .lesson-toc { order: -1; }
  .ledger-gate { grid-template-columns: 1fr; }
  .ledger-unlock { max-width: 620px; }
  .ledger-columns { grid-template-columns: 1fr; }
  .account-settings-grid { grid-template-columns: 1fr; }
}
@media (max-width: 780px) {
  .section-heading, .progress-panel, .practice-heading, .lesson-finish { align-items: start; grid-template-columns: 1fr; flex-direction: column; }
  .stat-grid { grid-template-columns: 1fr 1fr 1fr; }
  .lesson-row { grid-template-columns: 46px minmax(0,1fr) 36px; gap: 12px; }
  .lesson-meta { display: none; }
  .status-pill { position: absolute; width: 1px; height: 1px; padding: 0; margin: -1px; overflow: hidden; clip: rect(0,0,0,0); white-space: nowrap; border: 0; }
  .lesson-row { position: relative; }
  .lesson-row:has(.status-pill.complete) .row-arrow { background: var(--signal); border-color: var(--signal); color: #141a08; }
  .resource-grid { grid-template-columns: 1fr; }
  .lesson-score { text-align: left; }
  .source-sets-head, .source-set > header { align-items: start; flex-direction: column; }
  .ledger-header, .ledger-history-head { align-items: start; flex-direction: column; }
  .ledger-summary { grid-template-columns: 1fr; }
  .ledger-summary article { border-right: 0; border-bottom: 1px solid var(--line); }
  .payment-method-list { grid-template-columns: 1fr; }
  .session-row { grid-template-columns: 1fr auto; }
  .session-topic { grid-column: 1 / -1; grid-row: 2; }
  .session-actions { grid-column: 1 / -1; }
  .entry-row { grid-template-columns: 1fr auto; }
  .entry-row > button { grid-column: 1 / -1; width: fit-content; }
}
@media (max-width: 520px) {
  .stat-grid { grid-template-columns: 1fr; }
  .stat { border-left: 0; border-top: 1px solid var(--line); }
  .hero-copy h1 { font-size: 44px; }
  .lesson-hero h1, .subject-header h1 { font-size: 46px; }
  .lesson-figure { min-height: 220px; padding: 10px; }
  .ledger-gate-copy h1 { font-size: 44px; }
  .ledger-unlock, .payment-panel, .session-form-panel { padding: 20px; }
  .session-form-panel form { grid-template-columns: 1fr; }
  .session-form-panel .wide { grid-column: auto; }
}