:root {
  --bg: #f5f7fb;
  --panel: #ffffff;
  --panel-2: #f0f3f8;
  --text: #152033;
  --muted: #647086;
  --border: #dce2eb;
  --accent: #b51f2e;
  --accent-2: #7e1621;
  --accent-soft: #fbeaec;
  --good: #177245;
  --good-soft: #e8f7ef;
  --warn: #9b5d00;
  --warn-soft: #fff5df;
  --danger: #b42318;
  --code: #101827;
  --code-text: #e7edf7;
  --shadow: 0 8px 28px rgba(22, 32, 51, 0.08);
}

body.dark {
  --bg: #0e1420;
  --panel: #151e2d;
  --panel-2: #1b2637;
  --text: #eef3fb;
  --muted: #a6b1c2;
  --border: #2b394d;
  --accent: #ef5664;
  --accent-2: #ff7c88;
  --accent-soft: #3a2027;
  --good: #65d99b;
  --good-soft: #15362a;
  --warn: #f2b95f;
  --warn-soft: #3b2d14;
  --danger: #ff7b6f;
  --code: #0a0f18;
  --code-text: #e7edf7;
  --shadow: 0 8px 28px rgba(0,0,0,0.25);
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: Inter, ui-sans-serif, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  background: var(--bg);
  color: var(--text);
}
button, input, textarea, select { font: inherit; }
button { cursor: pointer; }
a { color: var(--accent); }

.app-shell { min-height: 100vh; display: grid; grid-template-columns: 278px minmax(0, 1fr); }
.sidebar {
  position: sticky; top: 0; height: 100vh; overflow-y: auto;
  background: var(--panel); border-right: 1px solid var(--border);
  padding: 20px 16px; display: flex; flex-direction: column; gap: 18px;
}
.brand { display: flex; gap: 12px; align-items: center; padding: 4px 8px 16px; border-bottom: 1px solid var(--border); }
.brand-mark { width: 42px; height: 42px; display: grid; place-items: center; border-radius: 12px; background: var(--accent); color: white; font-weight: 800; }
.brand strong { display: block; }
.brand span { color: var(--muted); font-size: 12px; display: block; margin-top: 2px; }
.nav-group-label { color: var(--muted); font-size: 11px; font-weight: 800; letter-spacing: .12em; margin: 14px 8px 6px; }
.nav-btn { width: 100%; border: 0; background: transparent; color: var(--text); text-align: left; padding: 10px 11px; border-radius: 10px; display: flex; align-items: center; justify-content: space-between; gap: 8px; }
.nav-btn:hover { background: var(--panel-2); }
.nav-btn.active { background: var(--accent-soft); color: var(--accent); font-weight: 750; }
.nav-btn .count { color: var(--muted); font-size: 11px; }
.sidebar-bottom { margin-top: auto; display: grid; gap: 8px; }

.main { min-width: 0; }
.topbar { position: sticky; top: 0; z-index: 10; background: color-mix(in srgb, var(--bg) 92%, transparent); backdrop-filter: blur(10px); border-bottom: 1px solid var(--border); padding: 18px 26px; display: flex; align-items: center; gap: 16px; }
.topbar h1 { margin: 2px 0 0; font-size: 24px; }
.eyebrow { color: var(--muted); font-size: 10px; letter-spacing: .14em; font-weight: 800; }
.top-actions { margin-left: auto; display: flex; align-items: center; gap: 10px; }
.icon-btn { display: none; background: var(--panel); border: 1px solid var(--border); width: 42px; height: 42px; border-radius: 10px; color: var(--text); }
.view { padding: 26px; max-width: 1380px; margin: 0 auto; }

.primary, .secondary, .ghost, .danger { border-radius: 10px; padding: 10px 14px; border: 1px solid transparent; font-weight: 700; }
.primary { background: var(--accent); color: white; }
.primary:hover { background: var(--accent-2); }
.secondary { background: var(--panel); color: var(--text); border-color: var(--border); }
.secondary:hover, .ghost:hover { background: var(--panel-2); }
.ghost { background: transparent; color: var(--text); border-color: var(--border); }
.danger { background: var(--danger); color: white; }
.wide { width: 100%; }
.danger-text { color: var(--danger); }
.pill { display: inline-flex; align-items: center; border-radius: 999px; background: var(--panel); border: 1px solid var(--border); padding: 8px 11px; color: var(--muted); font-size: 12px; font-weight: 700; }

.hero { display: grid; grid-template-columns: minmax(0, 1.3fr) minmax(280px, .7fr); gap: 18px; margin-bottom: 22px; }
.hero-card, .card { background: var(--panel); border: 1px solid var(--border); border-radius: 18px; box-shadow: var(--shadow); }
.hero-card { padding: 28px; }
.hero-card h2 { font-size: 31px; margin: 0 0 10px; line-height: 1.1; }
.hero-card p { color: var(--muted); line-height: 1.65; }
.hero-actions { display: flex; flex-wrap: wrap; gap: 10px; margin-top: 18px; }
.card { padding: 20px; }
.card h2, .card h3 { margin-top: 0; }
.stat-grid { display: grid; grid-template-columns: repeat(2, 1fr); gap: 12px; }
.stat { background: var(--panel-2); border-radius: 14px; padding: 18px; }
.stat .big { font-size: 28px; font-weight: 850; }
.stat .label { color: var(--muted); font-size: 12px; margin-top: 4px; }

.section-heading { display: flex; align-items: end; justify-content: space-between; gap: 12px; margin: 30px 0 12px; }
.section-heading h2 { margin: 0; }
.section-heading p { margin: 0; color: var(--muted); }
.module-grid { display: grid; grid-template-columns: repeat(3, minmax(0, 1fr)); gap: 14px; }
.module-card { background: var(--panel); border: 1px solid var(--border); border-radius: 16px; padding: 18px; display: flex; flex-direction: column; min-height: 205px; }
.module-card .tag { color: var(--accent); font-weight: 800; font-size: 11px; letter-spacing: .08em; }
.module-card h3 { margin: 8px 0 8px; }
.module-card p { color: var(--muted); line-height: 1.55; font-size: 14px; flex: 1; }
.module-card .meta { font-size: 12px; color: var(--muted); margin-bottom: 12px; }
.progress-line { width: 100%; height: 7px; background: var(--panel-2); border-radius: 999px; overflow: hidden; }
.progress-line > span { display: block; height: 100%; background: var(--accent); }

.lesson-layout { display: grid; grid-template-columns: 250px minmax(0, 1fr); gap: 18px; }
.lesson-index { background: var(--panel); border: 1px solid var(--border); border-radius: 16px; padding: 12px; align-self: start; position: sticky; top: 104px; max-height: calc(100vh - 130px); overflow: auto; }
.lesson-index button { width: 100%; text-align: left; border: 0; background: transparent; color: var(--text); border-radius: 9px; padding: 10px; }
.lesson-index button:hover { background: var(--panel-2); }
.lesson-index button.current { background: var(--accent-soft); color: var(--accent); font-weight: 750; }
.lesson-main { min-width: 0; }
.lesson-title { display: flex; align-items: start; justify-content: space-between; gap: 12px; margin-bottom: 14px; }
.lesson-title h2 { margin: 0; }
.lesson-title p { margin: 5px 0 0; color: var(--muted); }
.lesson-block { background: var(--panel); border: 1px solid var(--border); border-radius: 16px; padding: 22px; margin-bottom: 14px; }
.lesson-block h3 { margin-top: 0; }
.lesson-block p, .lesson-block li { line-height: 1.65; }
.lesson-block ul { padding-left: 22px; }
.callout { border-left: 4px solid var(--accent); padding: 12px 14px; background: var(--accent-soft); border-radius: 8px; margin: 14px 0; }
.exam-trap { border-left-color: var(--warn); background: var(--warn-soft); }
.source-note { margin-top: 12px; font-size: 12px; color: var(--muted); }

pre, code, textarea.code-input { font-family: "SFMono-Regular", Consolas, "Liberation Mono", monospace; }
pre { background: var(--code); color: var(--code-text); padding: 16px; border-radius: 12px; overflow-x: auto; line-height: 1.5; border: 1px solid color-mix(in srgb, var(--border) 50%, transparent); }
.code-inline { background: var(--panel-2); border: 1px solid var(--border); border-radius: 6px; padding: 1px 6px; font-size: .92em; }

.quiz-wrap { max-width: 900px; margin: 0 auto; }
.quiz-head { display: flex; align-items: center; gap: 12px; justify-content: space-between; margin-bottom: 14px; }
.timer { font-variant-numeric: tabular-nums; font-weight: 850; color: var(--accent); }
.question-card { background: var(--panel); border: 1px solid var(--border); border-radius: 16px; padding: 22px; margin-bottom: 14px; }
.question-card h3 { margin-top: 0; line-height: 1.4; }
.option { display: flex; gap: 10px; align-items: flex-start; padding: 11px; border: 1px solid var(--border); border-radius: 10px; margin: 8px 0; }
.option:hover { background: var(--panel-2); }
.option input { margin-top: 4px; }
.option.correct { border-color: var(--good); background: var(--good-soft); }
.option.wrong { border-color: var(--danger); background: color-mix(in srgb, var(--danger) 10%, var(--panel)); }
.explanation { margin-top: 12px; padding: 12px; border-radius: 10px; background: var(--panel-2); color: var(--muted); }

.flashcard-wrap { max-width: 760px; margin: 0 auto; text-align: center; }
.flashcard { min-height: 310px; display: grid; place-items: center; padding: 34px; background: var(--panel); border: 1px solid var(--border); border-radius: 22px; box-shadow: var(--shadow); }
.flashcard .face-label { color: var(--muted); font-size: 11px; letter-spacing: .12em; font-weight: 800; margin-bottom: 12px; }
.flashcard .content { font-size: 24px; line-height: 1.45; }
.flash-actions { display: flex; justify-content: center; gap: 10px; flex-wrap: wrap; margin-top: 16px; }

.playground-grid { display: grid; grid-template-columns: minmax(320px, .9fr) minmax(360px, 1.1fr); gap: 14px; }
.editor-panel, .preview-panel { background: var(--panel); border: 1px solid var(--border); border-radius: 16px; overflow: hidden; }
.panel-head { padding: 12px 14px; border-bottom: 1px solid var(--border); display: flex; align-items: center; justify-content: space-between; gap: 10px; }
.tabs { display: flex; gap: 6px; }
.tabs button { border: 1px solid var(--border); background: transparent; color: var(--text); border-radius: 8px; padding: 7px 10px; }
.tabs button.active { background: var(--accent-soft); color: var(--accent); border-color: color-mix(in srgb, var(--accent) 40%, var(--border)); }
.code-input { width: 100%; min-height: 520px; resize: vertical; border: 0; outline: 0; padding: 16px; background: var(--code); color: var(--code-text); line-height: 1.5; font-size: 14px; }
.preview { width: 100%; min-height: 570px; border: 0; background: white; }

.challenge-layout { display: grid; grid-template-columns: 300px minmax(0, 1fr); gap: 14px; }
.challenge-list { display: grid; gap: 8px; align-self: start; }
.challenge-btn { text-align: left; border: 1px solid var(--border); background: var(--panel); color: var(--text); border-radius: 12px; padding: 12px; }
.challenge-btn.active { border-color: var(--accent); background: var(--accent-soft); }
.challenge-btn.done::after { content: " ✓"; color: var(--good); font-weight: 900; }
.challenge-main { background: var(--panel); border: 1px solid var(--border); border-radius: 16px; overflow: hidden; }
.challenge-copy { padding: 20px; }
.challenge-copy p { color: var(--muted); line-height: 1.6; }
.challenge-editor { display: grid; grid-template-columns: 1fr 1fr; border-top: 1px solid var(--border); }
.challenge-editor textarea { min-height: 430px; resize: vertical; border: 0; padding: 14px; background: var(--code); color: var(--code-text); line-height: 1.5; outline: 0; font-family: Consolas, monospace; }
.challenge-editor iframe { width: 100%; min-height: 430px; border: 0; background: white; }
.feedback { padding: 12px 14px; border-top: 1px solid var(--border); color: var(--muted); }
.feedback.good { color: var(--good); background: var(--good-soft); }
.feedback.bad { color: var(--danger); }

.cheatsheet { display: grid; grid-template-columns: repeat(2, minmax(0, 1fr)); gap: 14px; }
.cheat-section { background: var(--panel); border: 1px solid var(--border); border-radius: 14px; padding: 18px; }
.cheat-section h3 { margin-top: 0; }
.cheat-section table { width: 100%; border-collapse: collapse; font-size: 13px; }
.cheat-section th, .cheat-section td { text-align: left; border-bottom: 1px solid var(--border); padding: 8px 6px; vertical-align: top; }
.cheat-section th { color: var(--muted); }

.search-box { width: 100%; max-width: 420px; padding: 11px 13px; border-radius: 10px; border: 1px solid var(--border); background: var(--panel); color: var(--text); }
.row { display: flex; gap: 10px; align-items: center; flex-wrap: wrap; }
.muted { color: var(--muted); }
.small { font-size: 12px; }
.hidden { display: none !important; }

#confirmDialog { border: 0; background: transparent; }
#confirmDialog::backdrop { background: rgba(0,0,0,.45); }
.dialog-card { width: min(460px, calc(100vw - 32px)); background: var(--panel); color: var(--text); border: 1px solid var(--border); border-radius: 16px; padding: 22px; box-shadow: var(--shadow); }
.dialog-card p { color: var(--muted); }
.dialog-actions { display: flex; justify-content: flex-end; gap: 10px; margin-top: 18px; }

@media (max-width: 1050px) {
  .module-grid { grid-template-columns: repeat(2, minmax(0, 1fr)); }
  .hero { grid-template-columns: 1fr; }
  .playground-grid { grid-template-columns: 1fr; }
  .challenge-layout { grid-template-columns: 1fr; }
  .challenge-list { grid-template-columns: repeat(2, minmax(0, 1fr)); }
}

@media (max-width: 820px) {
  .app-shell { grid-template-columns: 1fr; }
  .sidebar { position: fixed; z-index: 50; left: 0; top: 0; width: 278px; transform: translateX(-105%); transition: transform .2s ease; box-shadow: var(--shadow); }
  .sidebar.open { transform: translateX(0); }
  .icon-btn { display: grid; place-items: center; }
  .topbar { padding: 14px 16px; }
  .topbar h1 { font-size: 20px; }
  .progressPill { display: none; }
  .view { padding: 18px 14px; }
  .lesson-layout { grid-template-columns: 1fr; }
  .lesson-index { position: static; max-height: none; }
  .module-grid, .cheatsheet { grid-template-columns: 1fr; }
  .challenge-editor { grid-template-columns: 1fr; }
}

@media (max-width: 560px) {
  .top-actions .pill { display: none; }
  .top-actions .primary { padding: 9px 10px; }
  .hero-card { padding: 22px; }
  .hero-card h2 { font-size: 25px; }
  .module-grid { grid-template-columns: 1fr; }
  .challenge-list { grid-template-columns: 1fr; }
  .flashcard .content { font-size: 20px; }
  .stat-grid { grid-template-columns: 1fr 1fr; }
}

/* 2026 visual refresh */
:root {
  color-scheme: light;
  --bg: #f6f8fc;
  --panel: rgba(255, 255, 255, .94);
  --panel-solid: #ffffff;
  --panel-2: #f0f4fa;
  --text: #101828;
  --muted: #667085;
  --border: #dfe6f0;
  --accent: #635bff;
  --accent-2: #4f46e5;
  --accent-soft: #eeedff;
  --accent-glow: rgba(99, 91, 255, .20);
  --cyan: #0ea5a8;
  --good: #138a5b;
  --good-soft: #e8f8f1;
  --warn: #b96800;
  --warn-soft: #fff4dc;
  --danger: #d13f45;
  --code: #101827;
  --code-text: #edf3ff;
  --shadow: 0 16px 45px rgba(21, 31, 55, .08);
  --shadow-hover: 0 22px 52px rgba(27, 37, 67, .14);
}

html.dark-ready,
body.dark {
  color-scheme: dark;
  --bg: #0b1020;
  --panel: rgba(20, 27, 46, .94);
  --panel-solid: #141b2e;
  --panel-2: #1b253b;
  --text: #f3f6ff;
  --muted: #9ba9c3;
  --border: #2b3854;
  --accent: #938dff;
  --accent-2: #aca7ff;
  --accent-soft: #28264d;
  --accent-glow: rgba(147, 141, 255, .22);
  --cyan: #45d1d0;
  --good: #58d69f;
  --good-soft: #12362b;
  --warn: #ffc365;
  --warn-soft: #3b2d16;
  --danger: #ff858b;
  --code: #080d18;
  --code-text: #edf3ff;
  --shadow: 0 18px 50px rgba(0, 0, 0, .25);
  --shadow-hover: 0 24px 60px rgba(0, 0, 0, .38);
}

html.dark-ready body { background: #0b1020; }

body {
  min-height: 100vh;
  background:
    radial-gradient(circle at 78% -10%, var(--accent-glow), transparent 31rem),
    radial-gradient(circle at 104% 55%, color-mix(in srgb, var(--cyan) 8%, transparent), transparent 26rem),
    var(--bg);
  letter-spacing: -.008em;
  transition: background-color .25s ease, color .25s ease;
}

button, input, textarea, select { letter-spacing: inherit; }
button { transition: transform .16s ease, background-color .16s ease, border-color .16s ease, box-shadow .16s ease, color .16s ease; }
button:active { transform: translateY(1px); }
button:focus-visible, input:focus-visible, textarea:focus-visible, select:focus-visible, a:focus-visible {
  outline: 3px solid color-mix(in srgb, var(--accent) 42%, transparent);
  outline-offset: 2px;
}

.app-shell { grid-template-columns: 292px minmax(0, 1fr); }
.sidebar {
  background: color-mix(in srgb, var(--panel-solid) 88%, transparent);
  border-right-color: color-mix(in srgb, var(--border) 75%, transparent);
  padding: 22px 16px 18px;
  backdrop-filter: blur(20px) saturate(1.2);
}
.brand { padding: 2px 8px 20px; gap: 13px; }
.brand-mark {
  position: relative;
  width: 45px;
  height: 45px;
  overflow: hidden;
  border-radius: 14px;
  background: linear-gradient(145deg, #817aff, #5148e6 62%, #2f2a9d);
  box-shadow: 0 10px 24px var(--accent-glow), inset 0 1px rgba(255,255,255,.3);
}
.brand-mark::after {
  content: "";
  position: absolute;
  width: 32px;
  height: 32px;
  right: -16px;
  bottom: -16px;
  border-radius: 50%;
  background: #4ee1d0;
  opacity: .9;
}
.brand-mark span { position: relative; z-index: 1; }
.brand strong { font-size: 15px; letter-spacing: -.02em; }
.brand span { line-height: 1.4; }
.nav-group-label { margin-top: 17px; letter-spacing: .16em; font-size: 10px; }
.nav-btn { position: relative; min-height: 42px; padding: 10px 12px; border: 1px solid transparent; }
.nav-btn:hover { background: var(--panel-2); transform: translateX(2px); }
.nav-btn.active {
  background: linear-gradient(100deg, var(--accent-soft), color-mix(in srgb, var(--accent-soft) 35%, transparent));
  border-color: color-mix(in srgb, var(--accent) 20%, transparent);
  box-shadow: inset 3px 0 var(--accent);
}
.nav-btn .count { min-width: 32px; text-align: center; padding: 2px 6px; background: var(--panel-2); border-radius: 999px; }

.theme-toggle {
  display: grid;
  grid-template-columns: 22px 1fr auto;
  align-items: center;
  gap: 9px;
  padding: 9px 10px;
  border: 1px solid var(--border);
  border-radius: 12px;
  background: var(--panel-2);
  color: var(--text);
  text-align: left;
  font-size: 13px;
  font-weight: 700;
}
.theme-toggle:hover { border-color: color-mix(in srgb, var(--accent) 50%, var(--border)); }
.theme-icon { font-size: 16px; text-align: center; }
.theme-track { width: 36px; height: 20px; padding: 2px; border-radius: 999px; background: #cbd5e1; }
.theme-track span { display: block; width: 16px; height: 16px; border-radius: 50%; background: white; box-shadow: 0 2px 5px rgba(0,0,0,.2); transition: transform .22s ease; }
body.dark .theme-track { background: var(--accent); }
body.dark .theme-track span { transform: translateX(16px); }

.topbar {
  min-height: 82px;
  padding: 16px 30px;
  background: color-mix(in srgb, var(--bg) 78%, transparent);
  border-bottom-color: color-mix(in srgb, var(--border) 70%, transparent);
  backdrop-filter: blur(20px) saturate(1.35);
}
.topbar h1 { font-size: 25px; letter-spacing: -.035em; }
.eyebrow { color: var(--accent); letter-spacing: .16em; }
.view { padding: 32px 32px 52px; max-width: 1420px; }

.primary, .secondary, .ghost, .danger { border-radius: 11px; padding: 10px 15px; }
.primary {
  background: linear-gradient(135deg, var(--accent), var(--accent-2));
  box-shadow: 0 7px 18px color-mix(in srgb, var(--accent) 24%, transparent);
}
.primary:hover { background: linear-gradient(135deg, var(--accent-2), var(--accent)); box-shadow: 0 10px 24px color-mix(in srgb, var(--accent) 32%, transparent); transform: translateY(-1px); }
.secondary { background: var(--panel-solid); }
.secondary:hover, .ghost:hover { border-color: color-mix(in srgb, var(--accent) 35%, var(--border)); }
.pill { background: color-mix(in srgb, var(--panel-solid) 82%, transparent); box-shadow: 0 3px 12px rgba(20,30,50,.05); }

.hero { gap: 20px; margin-bottom: 28px; }
.hero-card, .card, .module-card, .lesson-block, .question-card, .editor-panel, .preview-panel, .challenge-main, .cheat-section {
  border-color: color-mix(in srgb, var(--border) 82%, transparent);
  box-shadow: var(--shadow);
}
.hero-card {
  position: relative;
  isolation: isolate;
  overflow: hidden;
  padding: 40px;
  background:
    linear-gradient(120deg, color-mix(in srgb, var(--panel-solid) 96%, transparent), color-mix(in srgb, var(--accent-soft) 64%, var(--panel-solid))),
    var(--panel-solid);
}
.hero-card::before {
  content: "</>";
  position: absolute;
  z-index: -1;
  right: -12px;
  top: -38px;
  color: color-mix(in srgb, var(--accent) 9%, transparent);
  font: 900 150px/1 ui-monospace, monospace;
  letter-spacing: -.18em;
  transform: rotate(-8deg);
}
.hero-card::after {
  content: "";
  position: absolute;
  inset: auto -50px -90px auto;
  z-index: -1;
  width: 210px;
  height: 210px;
  border: 34px solid color-mix(in srgb, var(--cyan) 11%, transparent);
  border-radius: 50%;
}
.hero-card h2 { max-width: 620px; margin-top: 18px; font-size: clamp(34px, 4vw, 52px); letter-spacing: -.055em; }
.hero-card p { max-width: 720px; font-size: 15px; }
.hero-kicker { display: flex; align-items: center; gap: 8px; color: var(--accent); font-size: 10px; font-weight: 850; letter-spacing: .16em; }
.live-dot { width: 8px; height: 8px; border-radius: 50%; background: var(--cyan); box-shadow: 0 0 0 5px color-mix(in srgb, var(--cyan) 14%, transparent); }
.topic-chips { display: flex; flex-wrap: wrap; gap: 7px; margin-top: 18px; }
.topic-chips span { padding: 5px 9px; border: 1px solid color-mix(in srgb, var(--accent) 22%, var(--border)); border-radius: 999px; background: color-mix(in srgb, var(--panel-solid) 70%, transparent); color: var(--muted); font-size: 11px; font-weight: 700; }
.hero-actions { margin-top: 24px; }

.progress-card { background: linear-gradient(155deg, var(--panel-solid), color-mix(in srgb, var(--panel-2) 70%, var(--panel-solid))); }
.progress-card-head { display: flex; align-items: center; justify-content: space-between; gap: 16px; margin-bottom: 18px; }
.progress-card-head h3 { margin: 5px 0 0; }
.progress-ring { position: relative; display: grid; place-items: center; width: 68px; height: 68px; border-radius: 50%; background: conic-gradient(var(--accent) var(--progress), var(--panel-2) 0); }
.progress-ring::before { content: ""; position: absolute; inset: 7px; border-radius: 50%; background: var(--panel-solid); }
.progress-ring span { position: relative; font-size: 14px; font-weight: 850; }
.stat { border: 1px solid color-mix(in srgb, var(--border) 70%, transparent); background: color-mix(in srgb, var(--panel-2) 78%, transparent); }
.stat .big { letter-spacing: -.045em; }

.section-heading { margin-top: 36px; }
.section-heading h2 { letter-spacing: -.035em; }
.module-grid { gap: 16px; }
.module-card { position: relative; overflow: hidden; padding: 20px; background: var(--panel); transition: transform .2s ease, box-shadow .2s ease, border-color .2s ease; }
.module-card::after { content: ""; position: absolute; width: 90px; height: 90px; right: -52px; top: -48px; border-radius: 50%; background: var(--accent-soft); transition: transform .25s ease; }
.module-card:hover { transform: translateY(-4px); border-color: color-mix(in srgb, var(--accent) 35%, var(--border)); box-shadow: var(--shadow-hover); }
.module-card:hover::after { transform: scale(1.25); }
.module-card-top { display: flex; align-items: center; justify-content: space-between; gap: 12px; }
.module-number { display: grid; place-items: center; width: 34px; height: 34px; border-radius: 10px; background: var(--accent-soft); color: var(--accent); font-size: 12px; font-weight: 850; }
.module-card .tag { margin-left: auto; }
.module-card h3 { font-size: 18px; letter-spacing: -.025em; }
.progress-line { height: 8px; }
.progress-line > span { background: linear-gradient(90deg, var(--accent), var(--cyan)); border-radius: inherit; }

.lesson-index, .flashcard { box-shadow: var(--shadow); }
.lesson-block { padding: 25px; }
.callout { border-left-width: 3px; }
pre { box-shadow: inset 0 1px rgba(255,255,255,.06), 0 8px 24px rgba(7,12,24,.12); }
.option { background: color-mix(in srgb, var(--panel-solid) 86%, transparent); }
.option:hover { border-color: color-mix(in srgb, var(--accent) 28%, var(--border)); }
.flashcard { background: linear-gradient(145deg, var(--panel-solid), color-mix(in srgb, var(--accent-soft) 38%, var(--panel-solid))); }
.flashcard:hover { transform: translateY(-2px); box-shadow: var(--shadow-hover); }
.search-box:focus { border-color: var(--accent); box-shadow: 0 0 0 4px var(--accent-glow); }

@media (max-width: 1050px) {
  .app-shell { grid-template-columns: 270px minmax(0, 1fr); }
  .hero-card { padding: 32px; }
}

@media (max-width: 820px) {
  .sidebar { width: 286px; }
  .topbar { min-height: 72px; padding: 13px 16px; }
  .view { padding: 22px 15px 40px; }
}

@media (max-width: 560px) {
  .hero-card { padding: 26px 22px; }
  .hero-card h2 { font-size: 34px; }
  .hero-card::before { font-size: 105px; opacity: .7; }
  .topic-chips { gap: 5px; }
  .progress-card-head { align-items: flex-start; }
}

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