:root {
  --bg: #e6ebe3;
  --bg-elev: #f7f9f4;
  --ink: #101a15;
  --ink-soft: #44584c;
  --line: #c7d0c2;
  --accent: #1b6b4a;
  --accent-soft: #d8efe4;
  --accent-2: #b85a22;
  --vn: #0b5a3b;
  --warn: #8a3b12;
  --lab: #1a4f6e;
  --sidebar: #0d1411;
  --sidebar-text: #d9e4db;
  --sidebar-muted: #7f9587;
  --slide-void: #070c09;
  --slide-card: #121c17;
  --gold: #d4a84b;
  --shadow: 0 20px 60px rgba(16, 26, 21, 0.14);
  --radius: 16px;
  --font-sans: "Be Vietnam Pro", system-ui, sans-serif;
  --font-display: "Literata", "Times New Roman", serif;
  --font-mono: "IBM Plex Mono", ui-monospace, monospace;
}

* { box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  margin: 0;
  font-family: var(--font-sans);
  color: var(--ink);
  background:
    radial-gradient(900px 480px at 0% -5%, rgba(27, 107, 74, 0.12), transparent 50%),
    radial-gradient(700px 420px at 100% 0%, rgba(184, 90, 34, 0.08), transparent 45%),
    linear-gradient(180deg, #eef2ea 0%, var(--bg) 40%, #e2e8de 100%);
  line-height: 1.68;
  -webkit-font-smoothing: antialiased;
}

::selection { background: rgba(27, 107, 74, 0.22); }

.app { display: flex; min-height: 100vh; }

/* —— Sidebar —— */
.sidebar {
  width: 300px;
  flex-shrink: 0;
  background:
    linear-gradient(165deg, rgba(27,107,74,0.18) 0%, transparent 35%),
    linear-gradient(180deg, #152019 0%, var(--sidebar) 55%, #0a100d 100%);
  color: var(--sidebar-text);
  padding: 1.15rem 0.9rem 2.5rem;
  overflow-y: auto;
  position: sticky;
  top: 0;
  height: 100vh;
  border-right: 1px solid #1e2c24;
  scrollbar-width: thin;
  scrollbar-color: #2a3d32 transparent;
}
.sidebar a {
  display: block;
  color: var(--sidebar-text);
  text-decoration: none;
  padding: 0.38rem 0.7rem;
  border-radius: 9px;
  font-size: 0.82rem;
  margin: 0.08rem 0;
  transition: background 0.15s, transform 0.15s;
}
.sidebar a:hover { background: rgba(255,255,255,0.07); transform: translateX(2px); }
.sidebar a.active {
  background: linear-gradient(90deg, rgba(27,107,74,0.45), rgba(27,107,74,0.18));
  color: #f0fff6;
  box-shadow: inset 3px 0 0 var(--gold);
  font-weight: 600;
}
.brand {
  font-family: var(--font-display) !important;
  font-weight: 700 !important;
  font-size: 1.2rem !important;
  letter-spacing: -0.025em;
  padding: 0.45rem 0.7rem 1.05rem !important;
  color: #f4fbf6 !important;
  line-height: 1.25 !important;
}
.brand::after {
  content: "HiếuTC · TLU · tự học";
  display: block;
  margin-top: 0.35rem;
  font-family: var(--font-sans);
  font-size: 0.68rem;
  font-weight: 500;
  letter-spacing: 0.06em;
  text-transform: uppercase;
  color: var(--sidebar-muted);
}
.nav-group { margin: 0.95rem 0 0.3rem; }
.nav-label {
  display: block;
  font-size: 0.66rem;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--sidebar-muted);
  padding: 0.4rem 0.7rem 0.25rem;
}
.sidebar-close { display: none; }

.main-wrap { flex: 1; min-width: 0; display: flex; flex-direction: column; }

/* —— Topbar —— */
.topbar {
  display: flex;
  align-items: flex-start;
  gap: 1rem;
  padding: 1rem 1.6rem 0.9rem;
  position: sticky;
  top: 0;
  z-index: 20;
  background: rgba(238, 242, 234, 0.82);
  backdrop-filter: blur(14px) saturate(1.2);
  border-bottom: 1px solid rgba(199, 208, 194, 0.85);
}
.top-titles { flex: 1; min-width: 0; }
.top-titles h1 {
  font-family: var(--font-display);
  font-size: clamp(1.2rem, 2.1vw, 1.7rem);
  line-height: 1.22;
  margin: 0;
  letter-spacing: -0.025em;
}
.subtitle { margin: 0.3rem 0 0; color: var(--ink-soft); font-size: 0.9rem; }
.menu-btn {
  display: none;
  border: 1px solid var(--line);
  background: var(--bg-elev);
  border-radius: 11px;
  width: 42px; height: 42px;
  font-size: 1.15rem;
  cursor: pointer;
}
.mode-toggle {
  display: flex;
  background: #d5ddd1;
  border-radius: 999px;
  padding: 3px;
  gap: 2px;
  box-shadow: inset 0 1px 2px rgba(0,0,0,0.06);
}
.mode-btn {
  border: 0;
  background: transparent;
  padding: 0.42rem 0.95rem;
  border-radius: 999px;
  font: inherit;
  font-size: 0.84rem;
  font-weight: 650;
  color: var(--ink-soft);
  cursor: pointer;
  transition: 0.15s;
}
.mode-btn.active {
  background: var(--ink);
  color: #f3f7f2;
  box-shadow: 0 4px 14px rgba(16,26,21,0.25);
}

.content {
  padding: 1.35rem 1.6rem 3rem;
  max-width: 940px;
  animation: fadeIn 0.35s ease;
}
@keyframes fadeIn {
  from { opacity: 0; transform: translateY(6px); }
  to { opacity: 1; transform: none; }
}

.content.mode-slide {
  max-width: none;
  padding: 0;
  background:
    radial-gradient(800px 500px at 20% 0%, rgba(27,107,74,0.22), transparent 55%),
    radial-gradient(700px 400px at 90% 80%, rgba(212,168,75,0.08), transparent 50%),
    var(--slide-void);
  color: #e8efe9;
  min-height: calc(100vh - 118px);
  animation: none;
}
.content.mode-slide .read-flow { display: none; }
.content.mode-read .slide-deck { display: none !important; }
.content.mode-slide .slide-deck { display: block; }

/* —— Slide chrome —— */
.slide-chrome {
  display: flex;
  align-items: center;
  gap: 0.75rem;
  padding: 0.7rem 1.5rem;
  background: rgba(7, 12, 9, 0.92);
  color: #cfe0d4;
  border-bottom: 1px solid #1e2f26;
  backdrop-filter: blur(8px);
}
.slide-chrome[hidden] { display: none !important; }
.slide-chrome button {
  border: 1px solid #355043;
  background: linear-gradient(180deg, #24362c, #1a2820);
  color: #e8efe9;
  border-radius: 11px;
  padding: 0.42rem 0.9rem;
  cursor: pointer;
  font: inherit;
  font-weight: 600;
  transition: 0.15s;
}
.slide-chrome button:hover { border-color: var(--gold); color: #fff; }
.slide-progress {
  flex: 1;
  height: 4px;
  background: #1e2c24;
  border-radius: 999px;
  overflow: hidden;
  max-width: 220px;
  margin: 0 0.35rem;
}
.slide-progress > i {
  display: block;
  height: 100%;
  width: 0%;
  background: linear-gradient(90deg, var(--accent), var(--gold));
  border-radius: inherit;
  transition: width 0.25s ease;
}
#slideCounter {
  font-variant-numeric: tabular-nums;
  font-size: 0.88rem;
  font-weight: 600;
  min-width: 4.5rem;
}
.slide-chrome .hint {
  margin-left: auto;
  font-size: 0.74rem;
  opacity: 0.65;
  letter-spacing: 0.02em;
}

/* —— Slides —— */
.slide {
  display: none;
  min-height: calc(100vh - 148px);
  padding: 2rem clamp(1rem, 4vw, 3.5rem);
  align-items: center;
  justify-content: center;
}
.slide.is-active {
  display: flex;
  animation: slideIn 0.32s cubic-bezier(0.22, 1, 0.36, 1);
}
@keyframes slideIn {
  from { opacity: 0; transform: translateY(16px) scale(0.985); }
  to { opacity: 1; transform: none; }
}
.slide-inner {
  width: min(980px, 100%);
  background:
    linear-gradient(145deg, rgba(27,107,74,0.14) 0%, transparent 40%),
    linear-gradient(165deg, #1a2820 0%, var(--slide-card) 55%, #0e1612 100%);
  border: 1px solid #2a3f34;
  border-radius: 26px;
  padding: clamp(1.5rem, 3.2vw, 2.6rem);
  box-shadow:
    0 0 0 1px rgba(212,168,75,0.06),
    0 40px 100px rgba(0,0,0,0.45);
  max-height: calc(100vh - 190px);
  overflow: auto;
  position: relative;
}
.slide-inner::before {
  content: "";
  position: absolute;
  top: 0; left: 2rem; right: 2rem;
  height: 2px;
  background: linear-gradient(90deg, transparent, var(--gold), transparent);
  opacity: 0.55;
}
.slide.slide-cover .slide-inner {
  text-align: left;
  background:
    linear-gradient(135deg, rgba(27,107,74,0.35) 0%, transparent 50%),
    linear-gradient(165deg, #1f3a2c 0%, #121c17 70%);
  min-height: min(420px, 60vh);
  display: flex;
  flex-direction: column;
  justify-content: center;
}
.slide-kicker {
  display: inline-block;
  font-size: 0.72rem;
  letter-spacing: 0.14em;
  text-transform: uppercase;
  color: var(--gold);
  font-weight: 650;
  margin-bottom: 0.75rem;
}
.mode-slide h1, .mode-slide h2, .mode-slide h3 { color: #f4fbf6; font-family: var(--font-display); }
.mode-slide h1 { font-size: clamp(1.8rem, 3.5vw, 2.6rem); letter-spacing: -0.03em; margin: 0 0 0.6rem; border: 0; padding: 0; }
.mode-slide h2 { font-size: clamp(1.35rem, 2.5vw, 1.85rem); border: 0; margin-top: 0; padding-top: 0; letter-spacing: -0.02em; }
.mode-slide h3 { font-size: 1.15rem; color: #9fd9b8; margin-top: 1.1rem; }
.mode-slide p, .mode-slide li, .mode-slide td { color: #d2e0d7; }
.mode-slide a { color: #9fd9b8; }
.mode-slide table {
  background: rgba(0,0,0,0.25);
  box-shadow: none;
  border-radius: 14px;
  overflow: hidden;
}
.mode-slide th { background: #24352c; color: #e8f5ec; }
.mode-slide td { border-color: #31463a; }
.mode-slide pre.ascii, .mode-slide pre {
  background: #070c09;
  border: 1px solid #355043;
  color: #c8e6d3;
  box-shadow: inset 0 0 40px rgba(27,107,74,0.08);
}
.mode-slide .callout {
  background: rgba(255,255,255,0.04);
  border-radius: 14px;
  border-left-width: 4px;
}
.mode-slide .callout-vn {
  background: linear-gradient(90deg, rgba(13,92,61,0.28), rgba(255,255,255,0.03));
  border-left-color: var(--gold);
}
.mode-slide .callout-fig {
  background: rgba(27,107,74,0.15);
  border-left-color: #6fc49a;
}
.mode-slide .callout-warn { background: rgba(138,59,18,0.2); border-left-color: #e09a6a; }
.mode-slide .callout-tip { background: rgba(212,168,75,0.12); border-left-color: var(--gold); }
.mode-slide .callout-lab { background: rgba(26,79,110,0.25); border-left-color: #6cb0d6; }
.mode-slide hr { border: 0; border-top: 1px solid #2a3f34; margin: 1.2rem 0; }

/* —— Read mode —— */
.read-flow h1 {
  font-family: var(--font-display);
  font-size: 2.05rem;
  letter-spacing: -0.03em;
  margin-top: 0;
}
.read-flow h2 {
  font-family: var(--font-display);
  font-size: 1.38rem;
  margin-top: 2.3rem;
  padding-top: 0.75rem;
  border-top: 1px solid var(--line);
  letter-spacing: -0.02em;
}
.read-flow h3 { font-size: 1.05rem; margin-top: 1.45rem; color: var(--accent); font-weight: 650; }

a { color: var(--accent); text-underline-offset: 2px; }
a:hover { color: var(--accent-2); }

table {
  width: 100%;
  border-collapse: collapse;
  font-size: 0.9rem;
  margin: 1rem 0 1.4rem;
  background: var(--bg-elev);
  border-radius: 14px;
  overflow: hidden;
  box-shadow: var(--shadow);
}
th, td {
  border: 1px solid var(--line);
  padding: 0.58rem 0.75rem;
  vertical-align: top;
}
th {
  background: linear-gradient(180deg, #e0eadc, #d4e0d0);
  text-align: left;
  font-weight: 650;
}

pre, pre.ascii {
  background: #152019;
  color: #d7ebe0;
  border: 1px solid #2c3c34;
  border-radius: 14px;
  padding: 1rem 1.1rem;
  overflow-x: auto;
  font-family: var(--font-mono);
  font-size: 0.78rem;
  line-height: 1.48;
  box-shadow: var(--shadow);
}
code {
  font-family: var(--font-mono);
  font-size: 0.86em;
  background: var(--accent-soft);
  color: #144532;
  padding: 0.12em 0.38em;
  border-radius: 6px;
}
pre code { background: transparent; padding: 0; color: inherit; }

blockquote {
  margin: 1.05rem 0;
  padding: 0.95rem 1.1rem;
  border-left: 4px solid var(--line);
  background: var(--bg-elev);
  border-radius: 0 14px 14px 0;
  box-shadow: 0 8px 24px rgba(16,26,21,0.04);
}
.callout-vn {
  border-left-color: var(--vn);
  background: linear-gradient(90deg, rgba(13,92,61,0.12), var(--bg-elev));
}
.callout-warn { border-left-color: var(--warn); background: #f8ebe3; }
.callout-tip { border-left-color: #b59a2f; background: #f5efd6; }
.callout-lab { border-left-color: var(--lab); background: #e7f1f6; }
.callout-fig { border-left-color: var(--accent); background: linear-gradient(90deg, var(--accent-soft), var(--bg-elev)); }
.callout-link { border-left-color: #4a6670; }

.katex-display { overflow-x: auto; overflow-y: hidden; padding: 0.25rem 0; }

/* —— Home —— */
.hero {
  position: relative;
  overflow: hidden;
  background:
    radial-gradient(600px 300px at 80% 20%, rgba(212,168,75,0.18), transparent 50%),
    linear-gradient(145deg, #12281e 0%, #1c4a34 42%, #243528 100%);
  color: #eef7f1;
  border-radius: 28px;
  padding: clamp(1.8rem, 4.5vw, 3.1rem);
  box-shadow: var(--shadow);
  margin-bottom: 1.85rem;
}
.hero::after {
  content: "";
  position: absolute;
  inset: auto -20% -40% auto;
  width: 280px; height: 280px;
  background: radial-gradient(circle, rgba(212,168,75,0.15), transparent 70%);
  pointer-events: none;
}
.hero .eyebrow {
  text-transform: uppercase;
  letter-spacing: 0.14em;
  font-size: 0.7rem;
  opacity: 0.78;
  margin: 0 0 0.7rem;
  font-weight: 650;
}
.hero h1 {
  font-family: var(--font-display);
  font-size: clamp(2.1rem, 4.8vw, 3.15rem);
  line-height: 1.08;
  margin: 0 0 0.9rem;
  color: #fff;
  border: 0;
  padding: 0;
  letter-spacing: -0.035em;
}
.hero .lede { max-width: 38rem; opacity: 0.93; font-size: 1.02rem; }
.hero-actions { display: flex; flex-wrap: wrap; gap: 0.65rem; margin-top: 1.4rem; position: relative; z-index: 1; }
.btn {
  display: inline-block;
  padding: 0.7rem 1.15rem;
  border-radius: 999px;
  border: 1px solid rgba(255,255,255,0.3);
  color: #fff !important;
  text-decoration: none;
  font-weight: 650;
  font-size: 0.9rem;
  background: rgba(255,255,255,0.07);
  transition: 0.15s;
}
.btn:hover { transform: translateY(-1px); background: rgba(255,255,255,0.14); }
.btn.primary {
  background: linear-gradient(180deg, #f3faf5, #dceee3);
  color: #123226 !important;
  border-color: transparent;
  box-shadow: 0 8px 24px rgba(0,0,0,0.2);
}

.home-grid h2, .home-note h2 {
  font-family: var(--font-display);
  border: 0;
  margin-top: 0.5rem;
  letter-spacing: -0.02em;
}
.chapters {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(230px, 1fr));
  gap: 1rem;
}
.chap-card {
  background: var(--bg-elev);
  border: 1px solid var(--line);
  border-radius: 18px;
  padding: 1.15rem 1.2rem;
  box-shadow: var(--shadow);
  transition: transform 0.18s, box-shadow 0.18s;
}
.chap-card:hover {
  transform: translateY(-3px);
  box-shadow: 0 24px 50px rgba(16,26,21,0.14);
}
.chap-card h3 {
  margin: 0 0 0.65rem;
  font-size: 1.02rem;
  color: var(--ink);
  font-family: var(--font-display);
}
.chap-card ol { margin: 0; padding-left: 1.1rem; font-size: 0.87rem; }
.chap-card a { text-decoration: none; font-weight: 500; }
.home-note {
  margin-top: 1.6rem;
  padding: 1.3rem 1.4rem;
  border-radius: 18px;
  background: linear-gradient(135deg, #e2ecd9, #d8e4d2);
  border: 1px solid var(--line);
}
.tiny { font-size: 0.85rem; color: var(--ink-soft); }
kbd {
  font-family: var(--font-mono);
  font-size: 0.78em;
  border: 1px solid #4a6356;
  background: #1a2820;
  color: #e8efe9;
  border-radius: 6px;
  padding: 0.08em 0.4em;
  box-shadow: 0 2px 0 #0a100c;
}
.mode-read kbd {
  border-color: var(--line);
  background: #eef2ea;
  color: var(--ink);
  box-shadow: 0 1px 0 #c5cec3;
}
.page-foot {
  padding: 1rem 1.6rem 2.2rem;
  color: var(--ink-soft);
  font-size: 0.8rem;
}
.pager {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin: 2.6rem 0 1rem;
  padding-top: 1.3rem;
  border-top: 1px solid var(--line);
}
.pager-link {
  font-weight: 650;
  text-decoration: none;
  padding: 0.72rem 1rem;
  border-radius: 14px;
  background: var(--bg-elev);
  border: 1px solid var(--line);
  box-shadow: 0 8px 20px rgba(16,26,21,0.06);
  transition: 0.15s;
}
.pager-link:hover {
  border-color: var(--accent);
  transform: translateY(-1px);
}

/* —— Teaching figures —— */
.fig-panel {
  margin: 1.6rem 0 2rem;
  padding: 1.2rem 1.25rem 1.4rem;
  border-radius: 20px;
  background: linear-gradient(145deg, #e8f0e4, var(--bg-elev));
  border: 1px solid var(--line);
  box-shadow: var(--shadow);
}
.fig-panel h2 {
  margin-top: 0 !important;
  border: 0 !important;
  padding-top: 0 !important;
  font-family: var(--font-display);
  font-size: 1.25rem !important;
}
.fig-note { color: var(--ink-soft); font-size: 0.92rem; margin: 0.35rem 0 1rem; }
.fig-grid {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(260px, 1fr));
  gap: 1rem;
}
.teach-fig {
  margin: 0;
  background: #0f1612;
  border-radius: 16px;
  overflow: hidden;
  border: 1px solid #2a3f34;
  box-shadow: 0 12px 30px rgba(16,26,21,0.12);
}
.teach-fig img {
  display: block;
  width: 100%;
  height: auto;
  background: #121c17;
}
.teach-fig figcaption {
  padding: 0.75rem 0.9rem 0.9rem;
  background: #152019;
  color: #d7e4db;
  font-size: 0.86rem;
  line-height: 1.45;
}
.teach-fig figcaption strong { display: block; color: #f2faf5; margin-bottom: 0.25rem; }
.teach-fig .credit { display: block; opacity: 0.7; font-size: 0.78rem; }
.mode-slide .fig-panel {
  background: transparent;
  border: 0;
  box-shadow: none;
  padding: 0;
}
.mode-slide .fig-panel h2 { color: #f4fbf6 !important; }
.mode-slide .fig-note { color: #9bb0a2; }
.mode-slide .teach-fig { box-shadow: 0 20px 50px rgba(0,0,0,0.35); }

body.slide-fullscreen .sidebar,
body.slide-fullscreen .topbar,
body.slide-fullscreen .page-foot { display: none; }
body.slide-fullscreen .slide-chrome { position: sticky; top: 0; z-index: 30; }
body.slide-fullscreen .slide { min-height: calc(100vh - 56px); }
body.slide-fullscreen .slide-inner { max-height: calc(100vh - 100px); }

@media (max-width: 960px) {
  .sidebar {
    position: fixed;
    z-index: 40;
    transform: translateX(-105%);
    transition: transform 0.22s ease;
    box-shadow: 20px 0 60px rgba(0,0,0,0.35);
  }
  .sidebar.open { transform: translateX(0); }
  .sidebar-close {
    display: block;
    margin: 0 0 0.5rem auto;
    background: transparent;
    border: 0;
    color: #fff;
    font-size: 1.6rem;
    cursor: pointer;
  }
  .menu-btn { display: inline-flex; align-items: center; justify-content: center; }
  .topbar { flex-wrap: wrap; }
  .slide-chrome .hint { display: none; }
}