:root {
  --font-sans: "Inter", "Segoe UI", system-ui, -apple-system, sans-serif;
  --font-mono: "Cascadia Code", "Fira Code", "Consolas", monospace;
  --radius-xs: 8px;
  --radius-sm: 12px;
  --radius-md: 18px;
  --radius-lg: 24px;
  --shadow-sm: 0 6px 18px rgba(16, 24, 40, 0.08);
  --shadow-md: 0 16px 42px rgba(16, 24, 40, 0.15);
  --shadow-lg: 0 28px 80px rgba(16, 24, 40, 0.2);
  --max-page: 1200px;
  --max-text: 94ch;
  --header-height: 68px;
}

@media (prefers-color-scheme: light) {
  :root {
    --bg: #f4f7ff;
    --bg-elevated: #ffffff;
    --bg-subtle: #eaf0ff;
    --text: #121826;
    --text-muted: #4b556b;
    --heading: #0d1424;
    --line: #d6def5;
    --accent: #405cf5;
    --accent-soft: #e6ebff;
    --ok: #047857;
  }
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #070b17;
    --bg-elevated: #0f1729;
    --bg-subtle: #16213a;
    --text: #e8edff;
    --text-muted: #a6b2cf;
    --heading: #f5f8ff;
    --line: #243250;
    --accent: #7ea3ff;
    --accent-soft: #1a2a56;
    --ok: #34d399;
  }
}

:root[data-theme="light"] {
  --bg: #f4f7ff;
  --bg-elevated: #ffffff;
  --bg-subtle: #eaf0ff;
  --text: #121826;
  --text-muted: #4b556b;
  --heading: #0d1424;
  --line: #d6def5;
  --accent: #405cf5;
  --accent-soft: #e6ebff;
  --ok: #047857;
}

:root[data-theme="dark"] {
  --bg: #070b17;
  --bg-elevated: #0f1729;
  --bg-subtle: #16213a;
  --text: #e8edff;
  --text-muted: #a6b2cf;
  --heading: #f5f8ff;
  --line: #243250;
  --accent: #7ea3ff;
  --accent-soft: #1a2a56;
  --ok: #34d399;
}

* {
  box-sizing: border-box;
}

html {
  color-scheme: light dark;
  scroll-behavior: smooth;
}

body {
  margin: 0;
  font-family: var(--font-sans);
  color: var(--text);
  line-height: 1.65;
  background:
    radial-gradient(circle at 10% -20%, color-mix(in srgb, var(--accent) 18%, transparent) 0%, transparent 48%),
    radial-gradient(circle at 95% 10%, color-mix(in srgb, var(--ok) 15%, transparent) 0%, transparent 38%),
    var(--bg);
  min-height: 100vh;
}

a {
  color: var(--accent);
}

a:hover {
  text-decoration-thickness: 2px;
}

img,
svg,
video {
  max-width: 100%;
}

code,
pre {
  font-family: var(--font-mono);
}

.skip-link {
  position: absolute;
  left: 1rem;
  top: -100px;
  z-index: 999;
  background: var(--accent);
  color: #fff;
  padding: 0.6rem 0.9rem;
  border-radius: var(--radius-xs);
  text-decoration: none;
}

.skip-link:focus-visible {
  top: 1rem;
}

:focus-visible {
  outline: 3px solid color-mix(in srgb, var(--accent) 55%, white 10%);
  outline-offset: 3px;
  border-radius: 6px;
}

.site-shell {
  width: min(100% - 2rem, var(--max-page));
  margin: 0 auto;
}

.site-header {
  position: sticky;
  top: 0;
  z-index: 50;
  backdrop-filter: blur(16px);
  background: color-mix(in srgb, var(--bg) 72%, transparent);
  border-bottom: 1px solid color-mix(in srgb, var(--line) 74%, transparent);
}

.site-nav {
  min-height: var(--header-height);
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 1rem;
}

.brand {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  text-decoration: none;
  color: var(--heading);
  font-weight: 700;
  letter-spacing: 0.2px;
}

.brand-mark {
  width: 30px;
  height: 30px;
  border-radius: 9px;
  display: grid;
  place-items: center;
  color: #fff;
  background: linear-gradient(145deg, var(--accent), color-mix(in srgb, var(--accent) 62%, #8ef6ff));
  box-shadow: var(--shadow-sm);
  font-size: 0.9rem;
}

.nav-links {
  display: flex;
  align-items: center;
  gap: 0.45rem;
}

.nav-links a {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  min-height: 36px;
  padding: 0 0.85rem;
  border-radius: 999px;
  border: 1px solid transparent;
  text-decoration: none;
  color: var(--text-muted);
  font-weight: 600;
  font-size: 0.94rem;
}

.nav-links a:hover,
.nav-links a[aria-current="page"] {
  color: var(--heading);
  background: var(--accent-soft);
  border-color: color-mix(in srgb, var(--accent) 35%, transparent);
}

.nav-right {
  display: flex;
  align-items: center;
  gap: 0.6rem;
}

.theme-toggle {
  display: inline-flex;
  align-items: center;
  border: 1px solid var(--line);
  border-radius: 999px;
  padding: 0.15rem;
  background: var(--bg-elevated);
}

.theme-toggle button {
  border: 0;
  min-height: 30px;
  min-width: 46px;
  padding: 0 0.55rem;
  border-radius: 999px;
  color: var(--text-muted);
  background: transparent;
  font-weight: 600;
  font-size: 0.78rem;
  cursor: pointer;
}

.theme-toggle button.active {
  background: var(--accent-soft);
  color: var(--heading);
}

.page-main {
  padding: 2rem 0 3rem;
}

.hero {
  background: linear-gradient(160deg, color-mix(in srgb, var(--accent-soft) 60%, transparent), color-mix(in srgb, var(--bg-elevated) 74%, transparent));
  border: 1px solid var(--line);
  border-radius: var(--radius-lg);
  padding: clamp(1.4rem, 3vw, 2.6rem);
  box-shadow: var(--shadow-md);
}

.kicker {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.82rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: var(--text-muted);
  margin: 0 0 0.75rem;
}

h1,
h2,
h3,
h4 {
  margin-top: 0;
  color: var(--heading);
  line-height: 1.22;
}

.hero h1 {
  font-size: clamp(1.9rem, 4.4vw, 3rem);
  margin-bottom: 0.9rem;
}

.hero p {
  margin: 0;
  max-width: 62ch;
  color: var(--text-muted);
}

.cta-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.8rem;
  margin-top: 1.4rem;
}

.btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  min-height: 42px;
  padding: 0 1rem;
  border-radius: 999px;
  border: 1px solid var(--line);
  text-decoration: none;
  font-weight: 600;
  color: var(--heading);
  background: var(--bg-elevated);
}

.btn.primary {
  background: var(--accent);
  color: #fff;
  border-color: color-mix(in srgb, var(--accent) 64%, black 10%);
}

.stats-grid,
.path-grid,
.roadmap-grid,
.track-grid {
  display: grid;
  gap: 1rem;
}

.stats-grid {
  grid-template-columns: repeat(auto-fit, minmax(150px, 1fr));
  margin-top: 1.4rem;
}

.stat-card,
.path-card,
.panel,
.slide-card,
.roadmap-card,
.track-card {
  background: var(--bg-elevated);
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
}

.stat-card {
  padding: 0.95rem;
}

.stat-card strong {
  display: block;
  font-size: 1.6rem;
  line-height: 1;
  margin-bottom: 0.35rem;
}

.stat-card span {
  color: var(--text-muted);
  font-size: 0.9rem;
}

.section {
  margin-top: 2rem;
}

.section h2 {
  font-size: clamp(1.35rem, 2.2vw, 1.8rem);
  margin-bottom: 0.25rem;
}

.section > p {
  margin-top: 0;
  color: var(--text-muted);
}

.path-grid {
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
}

.path-card,
.track-card,
.slide-card,
.roadmap-card {
  padding: 1rem;
}

.path-card h3,
.track-card h3,
.slide-card h3,
.roadmap-card h3 {
  margin-bottom: 0.45rem;
  font-size: 1.02rem;
}

.path-card p,
.track-card p,
.slide-card p,
.roadmap-card p {
  margin: 0;
  color: var(--text-muted);
  font-size: 0.93rem;
}

.path-card,
.slide-card,
.track-card {
  text-decoration: none;
  color: inherit;
  transition: transform 0.16s ease, border-color 0.16s ease, box-shadow 0.16s ease;
}

.path-card:hover,
.slide-card:hover,
.track-card:hover {
  transform: translateY(-2px);
  border-color: color-mix(in srgb, var(--accent) 38%, var(--line));
  box-shadow: var(--shadow-md);
}

.study-order {
  margin-top: 0.8rem;
  padding: 1rem;
  border-radius: var(--radius-md);
  border: 1px dashed color-mix(in srgb, var(--accent) 42%, var(--line));
  background: color-mix(in srgb, var(--accent-soft) 58%, var(--bg-elevated));
}

.study-order ol {
  margin: 0.5rem 0 0;
  padding-left: 1.25rem;
  column-gap: 2rem;
}

.study-order li {
  margin-bottom: 0.35rem;
}

.slides-controls {
  margin-top: 1.1rem;
  display: grid;
  gap: 0.85rem;
}

.search-input {
  width: min(100%, 700px);
  min-height: 44px;
  border-radius: 12px;
  border: 1px solid var(--line);
  background: var(--bg-elevated);
  color: var(--text);
  font: inherit;
  padding: 0 0.95rem;
}

.filter-row {
  display: flex;
  flex-wrap: wrap;
  gap: 0.5rem;
}

.filter-chip {
  min-height: 34px;
  padding: 0 0.8rem;
  border-radius: 999px;
  border: 1px solid var(--line);
  background: var(--bg-elevated);
  color: var(--text-muted);
  font-weight: 600;
  cursor: pointer;
}

.filter-chip.active {
  color: var(--heading);
  border-color: color-mix(in srgb, var(--accent) 38%, var(--line));
  background: var(--accent-soft);
}

.results-line {
  color: var(--text-muted);
  font-size: 0.9rem;
}

.track-grid {
  margin-top: 1.2rem;
}

.track-card {
  padding-bottom: 1.15rem;
}

.track-header {
  display: flex;
  flex-wrap: wrap;
  justify-content: space-between;
  gap: 0.5rem;
  margin-bottom: 0.8rem;
}

.track-title {
  margin: 0;
  font-size: 1.12rem;
}

.track-rationale {
  margin: 0;
  color: var(--text-muted);
  font-size: 0.9rem;
}

.slide-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
  gap: 0.8rem;
}

.slide-meta {
  margin-top: 0.6rem;
  display: flex;
  gap: 0.35rem;
  flex-wrap: wrap;
}

.tag {
  display: inline-flex;
  align-items: center;
  min-height: 24px;
  padding: 0 0.52rem;
  border-radius: 999px;
  font-size: 0.76rem;
  font-weight: 650;
  color: var(--text-muted);
  background: color-mix(in srgb, var(--bg-subtle) 78%, var(--bg-elevated));
  border: 1px solid color-mix(in srgb, var(--line) 90%, transparent);
}

.empty-state {
  margin-top: 1rem;
  padding: 1rem;
  border-radius: var(--radius-sm);
  background: color-mix(in srgb, var(--bg-subtle) 60%, var(--bg-elevated));
  border: 1px dashed var(--line);
  color: var(--text-muted);
}

.breadcrumb {
  margin-bottom: 1rem;
  color: var(--text-muted);
  font-size: 0.9rem;
}

.breadcrumb a {
  text-decoration: none;
}

.reading-progress {
  position: fixed;
  top: 0;
  left: 0;
  width: 100%;
  height: 3px;
  z-index: 70;
  background: linear-gradient(90deg, var(--accent), color-mix(in srgb, var(--accent) 35%, #7efac6));
  transform-origin: left center;
  transform: scaleX(0);
  transition: transform 0.14s linear;
}

.study-layout {
  display: grid;
  gap: 1.2rem;
  grid-template-columns: minmax(0, 1fr);
}

.study-page-header {
  padding: 1.15rem;
  background: var(--bg-elevated);
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
}

.study-page-header h1 {
  margin-bottom: 0.65rem;
  font-size: clamp(1.45rem, 2.6vw, 2.1rem);
}

.study-page-header p {
  margin-top: 0;
  color: var(--text-muted);
  max-width: var(--max-text);
}

.meta-grid {
  margin-top: 0.9rem;
  display: grid;
  gap: 0.75rem;
  grid-template-columns: repeat(auto-fit, minmax(220px, 1fr));
}

.study-tools {
  margin-top: 0.8rem;
  padding: 0.75rem;
  border: 1px solid color-mix(in srgb, var(--accent) 32%, var(--line));
  border-radius: var(--radius-sm);
  background: color-mix(in srgb, var(--accent-soft) 72%, var(--bg-elevated));
}

.study-mode-toggle {
  border: 1px solid color-mix(in srgb, var(--accent) 40%, var(--line));
  background: var(--bg-elevated);
  color: var(--heading);
  border-radius: 999px;
  min-height: 36px;
  padding: 0 0.95rem;
  font-weight: 700;
  cursor: pointer;
}

.study-mode-toggle[aria-pressed="true"] {
  background: var(--accent);
  color: #fff;
  border-color: color-mix(in srgb, var(--accent) 66%, black 8%);
}

.study-tools-hint {
  margin: 0.5rem 0 0;
  color: var(--text-muted);
  font-size: 0.88rem;
}

.meta-card {
  background: color-mix(in srgb, var(--bg-subtle) 58%, var(--bg-elevated));
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  padding: 0.75rem;
}

.meta-card h2 {
  margin: 0 0 0.35rem;
  font-size: 0.95rem;
}

.meta-card p,
.meta-card ul {
  margin: 0;
  color: var(--text-muted);
  font-size: 0.9rem;
}

.meta-card ul {
  padding-left: 1.1rem;
}

.study-content-wrap {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 1rem;
}

.study-article {
  max-width: var(--max-text);
  padding: clamp(1rem, 2.4vw, 1.6rem);
  background: var(--bg-elevated);
  border: 1px solid var(--line);
  border-radius: var(--radius-md);
  box-shadow: var(--shadow-sm);
}

.study-article h1,
.study-article h2,
.study-article h3 {
  scroll-margin-top: calc(var(--header-height) + 20px);
}

.study-article h1 {
  margin-top: 1.8rem;
  margin-bottom: 0.8rem;
  font-size: clamp(1.25rem, 2.2vw, 1.56rem);
  border-bottom: 1px solid var(--line);
  padding-bottom: 0.4rem;
}

.study-article h1:first-child {
  margin-top: 0;
}

.study-article h2 {
  margin-top: 1.55rem;
  margin-bottom: 0.65rem;
  font-size: clamp(1.15rem, 2vw, 1.35rem);
}

.study-article h3 {
  margin-top: 1.2rem;
  margin-bottom: 0.55rem;
  font-size: 1.02rem;
}

.study-article p,
.study-article li,
.study-article td,
.study-article th {
  color: var(--text);
}

.study-article p {
  margin-top: 0;
  margin-bottom: 0.95rem;
}

.study-article ul,
.study-article ol {
  margin-top: 0;
  margin-bottom: 1rem;
  padding-left: 1.3rem;
}

.study-article li {
  margin-bottom: 0.35rem;
}

.study-article table {
  width: 100%;
  border-collapse: collapse;
  display: block;
  overflow-x: auto;
  margin-bottom: 1rem;
  border: 1px solid var(--line);
  border-radius: var(--radius-xs);
}

.study-article th,
.study-article td {
  min-width: 180px;
  border-bottom: 1px solid var(--line);
  padding: 0.55rem;
  font-size: 0.92rem;
  vertical-align: top;
}

.study-article th {
  text-align: left;
  background: color-mix(in srgb, var(--bg-subtle) 66%, var(--bg-elevated));
}

.study-article code {
  border: 1px solid color-mix(in srgb, var(--line) 84%, transparent);
  border-radius: 6px;
  padding: 0.1rem 0.35rem;
  background: color-mix(in srgb, var(--bg-subtle) 68%, var(--bg-elevated));
}

.study-article pre {
  margin: 0.8rem 0 1rem;
  border: 1px solid var(--line);
  border-radius: var(--radius-xs);
  padding: 0.8rem;
  overflow-x: auto;
  background: color-mix(in srgb, var(--bg-subtle) 65%, var(--bg-elevated));
}

.study-article pre code {
  border: 0;
  background: transparent;
  padding: 0;
}

.study-section {
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  background: color-mix(in srgb, var(--bg-subtle) 40%, var(--bg-elevated));
  margin-bottom: 0.9rem;
  overflow: clip;
}

.study-section-summary {
  display: flex;
  align-items: center;
  gap: 0.5rem;
  cursor: pointer;
  list-style: none;
  padding: 0.7rem 0.9rem;
  border-bottom: 1px solid transparent;
}

.study-section[open] > .study-section-summary {
  border-bottom-color: var(--line);
}

.study-section-summary::-webkit-details-marker {
  display: none;
}

.study-section-summary::before {
  content: "\25B8";
  color: var(--text-muted);
  font-size: 0.82rem;
  line-height: 1;
  transform-origin: center;
  transition: transform 0.14s ease;
}

.study-section[open] > .study-section-summary::before {
  transform: rotate(90deg);
}

.study-section-title {
  margin: 0;
  border: 0 !important;
  padding: 0 !important;
  font-size: clamp(1.05rem, 1.7vw, 1.26rem) !important;
}

.study-section-body {
  padding: 0.85rem 0.95rem 0.95rem;
}

.study-section-body > :last-child {
  margin-bottom: 0;
}

.section-detail-toggle {
  display: none;
  border: 1px solid var(--line);
  border-radius: 999px;
  min-height: 32px;
  padding: 0 0.7rem;
  margin-bottom: 0.7rem;
  font-size: 0.82rem;
  font-weight: 700;
  color: var(--heading);
  background: color-mix(in srgb, var(--bg-subtle) 62%, var(--bg-elevated));
  cursor: pointer;
}

.exam-progress {
  margin: 0 0 0.65rem;
  padding: 0.5rem 0.6rem;
  border: 1px solid color-mix(in srgb, var(--line) 85%, transparent);
  border-radius: var(--radius-xs);
  background: color-mix(in srgb, var(--bg-subtle) 55%, var(--bg-elevated));
  color: var(--text-muted);
  font-size: 0.85rem;
  font-weight: 600;
}

.exam-list {
  list-style: none;
  padding-left: 0 !important;
  display: grid;
  gap: 0.7rem;
}

.exam-card {
  margin: 0;
  padding: 0.75rem;
  border: 1px solid var(--line);
  border-radius: var(--radius-xs);
  background: var(--bg-elevated);
}

.exam-question {
  font-weight: 600;
}

.exam-answer {
  margin-top: 0.6rem;
  padding: 0.6rem 0.7rem;
  border: 1px dashed color-mix(in srgb, var(--line) 90%, transparent);
  border-radius: var(--radius-xs);
  background: color-mix(in srgb, var(--bg-subtle) 60%, var(--bg-elevated));
  color: var(--text-muted);
}

.exam-controls {
  margin-top: 0.65rem;
  display: flex;
  flex-wrap: wrap;
  gap: 0.45rem;
}

.exam-btn {
  border: 1px solid var(--line);
  border-radius: 999px;
  min-height: 30px;
  padding: 0 0.7rem;
  font-size: 0.8rem;
  font-weight: 700;
  color: var(--heading);
  background: var(--bg-elevated);
  cursor: pointer;
}

.exam-btn.reveal {
  border-color: color-mix(in srgb, var(--accent) 34%, var(--line));
}

.exam-btn.mark.active {
  color: #fff;
}

.exam-btn.mark.known.active {
  background: #0f9d58;
  border-color: #0f9d58;
}

.exam-btn.mark.unknown.active {
  background: #c2410c;
  border-color: #c2410c;
}

.study-mode .section-detail-toggle {
  display: inline-flex;
  align-items: center;
}

.study-mode .study-section:not(.show-details) [data-study-detail="true"] {
  display: none;
}

.toc {
  position: sticky;
  top: calc(var(--header-height) + 1rem);
  align-self: start;
  background: var(--bg-elevated);
  border: 1px solid var(--line);
  border-radius: var(--radius-sm);
  padding: 0.85rem;
  box-shadow: var(--shadow-sm);
}

.toc h2 {
  margin: 0 0 0.5rem;
  font-size: 0.92rem;
}

.toc ul {
  list-style: none;
  margin: 0;
  padding: 0;
  display: grid;
  gap: 0.35rem;
}

.toc a {
  display: block;
  color: var(--text-muted);
  text-decoration: none;
  font-size: 0.86rem;
  border-radius: 8px;
  padding: 0.25rem 0.45rem;
}

.toc a.active {
  color: var(--heading);
  background: var(--accent-soft);
}

.page-nav {
  margin-top: 1rem;
  max-width: var(--max-text);
  display: flex;
  flex-wrap: wrap;
  gap: 0.65rem;
}

.page-nav a {
  flex: 1 1 220px;
  padding: 0.75rem 0.9rem;
  text-decoration: none;
  border-radius: var(--radius-sm);
  border: 1px solid var(--line);
  background: var(--bg-elevated);
  color: var(--text);
}

.page-nav a span {
  display: block;
  font-size: 0.78rem;
  color: var(--text-muted);
}

.callout {
  margin-top: 0.9rem;
  border: 1px solid color-mix(in srgb, var(--accent) 32%, var(--line));
  border-radius: var(--radius-sm);
  background: color-mix(in srgb, var(--accent-soft) 70%, var(--bg-elevated));
  padding: 0.8rem;
  max-width: var(--max-text);
  color: var(--text-muted);
}

.roadmap-grid {
  grid-template-columns: repeat(auto-fit, minmax(200px, 1fr));
}

.muted {
  color: var(--text-muted);
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  border: 0;
}

@media (min-width: 1060px) {
  .study-content-wrap {
    grid-template-columns: minmax(0, 1fr) 230px;
  }

  .study-content-wrap .toc {
    grid-column: 2;
    grid-row: 1;
  }

  .study-content-wrap .study-article,
  .study-content-wrap .page-nav,
  .study-content-wrap .callout {
    grid-column: 1;
  }
}

@media (max-width: 760px) {
  .site-shell {
    width: min(100% - 1rem, var(--max-page));
  }

  .site-nav {
    flex-wrap: wrap;
    justify-content: center;
    padding: 0.6rem 0;
  }

  .nav-right {
    width: 100%;
    justify-content: center;
  }

  .hero {
    border-radius: var(--radius-md);
  }

  .study-order ol {
    columns: 1;
  }
}