/* ── React / TypeScript Tutorial — Modern Dark Design ── */
:root {
  --react-blue: #61DAFB;
  --react-blue-dim: #21a1c4;
  --ts-blue: #3178C6;
  --ts-blue-light: #4A90D9;
  --dark-bg: #0A0E1A;
  --dark-surface: #111827;
  --dark-card: #1A2235;
  --dark-card-hover: #1F2A42;
  --dark-border: rgba(255,255,255,0.08);
  --dark-border-bright: rgba(97,218,251,0.25);
  --text-primary: #E8EAF0;
  --text-secondary: #8896A8;
  --text-muted: #56637A;
  --green: #4ADE80;
  --orange: #FB923C;
  --red: #F87171;
  --purple: #C084FC;
  --yellow: #FBBF24;
  --radius: 10px;
  --radius-lg: 14px;
}

* { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }
body {
  font-family: -apple-system, 'Inter', 'Segoe UI', sans-serif;
  background: var(--dark-bg);
  color: var(--text-primary);
  line-height: 1.65;
  -webkit-font-smoothing: antialiased;
}

/* ── NAV ── */
.nav {
  position: sticky; top: 0; z-index: 100;
  background: rgba(10,14,26,0.9);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--dark-border);
  padding: 0 24px; height: 54px;
  display: flex; align-items: center; gap: 16px;
}
.nav-back {
  color: var(--react-blue); text-decoration: none;
  font-size: 0.9rem; display: flex; align-items: center; gap: 4px;
}
.nav-back::before { content: '‹'; font-size: 1.3rem; }
.nav-title { font-size: 0.95rem; font-weight: 600; flex: 1; color: var(--text-primary); }
.nav-badge {
  background: linear-gradient(135deg, var(--react-blue), var(--ts-blue));
  color: #fff; font-size: 0.65rem; font-weight: 700;
  padding: 3px 10px; border-radius: 20px;
}

/* ── HERO ── */
.hero {
  background: radial-gradient(ellipse 80% 60% at 50% 0%, rgba(97,218,251,0.08) 0%, transparent 60%),
              var(--dark-surface);
  padding: 80px 24px 70px;
  text-align: center;
  border-bottom: 1px solid var(--dark-border);
  position: relative;
  overflow: hidden;
}
.hero::before {
  content: '';
  position: absolute; inset: 0;
  background: radial-gradient(circle 400px at 20% 50%, rgba(49,120,198,0.06) 0%, transparent 70%);
}
.hero-icon {
  font-size: 4rem; margin-bottom: 16px;
  animation: spin 20s linear infinite;
  display: inline-block;
}
@keyframes spin { from { transform: rotate(0deg); } to { transform: rotate(360deg); } }
.hero-eyebrow {
  font-size: 0.72rem; font-weight: 700; letter-spacing: 0.2em;
  text-transform: uppercase; color: var(--react-blue); margin-bottom: 12px;
  position: relative;
}
.hero h1 {
  font-size: clamp(2rem, 5vw, 3.4rem); font-weight: 800;
  letter-spacing: -0.03em; line-height: 1.15; position: relative;
  background: linear-gradient(135deg, var(--react-blue) 0%, var(--text-primary) 50%, var(--ts-blue-light) 100%);
  -webkit-background-clip: text; -webkit-text-fill-color: transparent; background-clip: text;
  margin-bottom: 16px;
}
.hero-sub { font-size: 1rem; color: var(--text-secondary); max-width: 540px; margin: 0 auto 28px; position: relative; }
.hero-chips { display: flex; flex-wrap: wrap; gap: 8px; justify-content: center; position: relative; }
.chip {
  background: rgba(255,255,255,0.06); border: 1px solid var(--dark-border-bright);
  color: var(--text-secondary); font-size: 0.75rem; padding: 4px 12px; border-radius: 20px;
  font-family: 'SF Mono', Consolas, monospace;
}

/* ── CONTAINER ── */
.container { max-width: 860px; margin: 0 auto; padding: 32px 24px 80px; }

/* ── CARDS ── */
.card {
  background: var(--dark-card); border: 1px solid var(--dark-border);
  border-radius: var(--radius-lg); padding: 22px; margin-bottom: 14px;
}
.card-list { list-style: none; }
.card-list li { border-bottom: 1px solid var(--dark-border); }
.card-list li:last-child { border-bottom: none; }
.card-list a {
  display: flex; align-items: flex-start; gap: 14px;
  padding: 14px 12px; text-decoration: none; color: inherit;
  border-radius: var(--radius); transition: background 0.15s;
}
.card-list a:hover { background: var(--dark-card-hover); }
.list-num {
  width: 28px; height: 28px; background: linear-gradient(135deg, var(--react-blue), var(--ts-blue));
  color: #000; border-radius: 50%; display: flex; align-items: center;
  justify-content: center; font-size: 0.72rem; font-weight: 800; flex-shrink: 0;
}
.list-content { flex: 1; }
.list-title { font-size: 0.95rem; font-weight: 600; color: var(--text-primary); margin-bottom: 3px; }
.list-desc { font-size: 0.8rem; color: var(--text-muted); }
.list-chevron { color: var(--text-muted); font-size: 1rem; align-self: center; }

.section-label {
  font-size: 0.7rem; font-weight: 700; letter-spacing: 0.12em;
  text-transform: uppercase; color: var(--text-muted); margin: 28px 0 10px 2px;
}

/* ── CHAPTER PAGE ── */
.chapter-hero {
  background: linear-gradient(135deg, #0F1929 0%, #1A2235 100%);
  border-bottom: 1px solid var(--dark-border-bright);
  padding: 56px 24px 48px; text-align: center;
}
.chapter-hero .ch-num {
  font-size: 0.7rem; font-weight: 700; letter-spacing: 0.2em;
  text-transform: uppercase; color: var(--react-blue); margin-bottom: 10px;
  font-family: 'SF Mono', monospace;
}
.chapter-hero h1 {
  font-size: clamp(1.8rem, 4vw, 2.6rem); font-weight: 800; letter-spacing: -0.02em;
  margin-bottom: 14px; color: var(--text-primary);
}
.chapter-hero p { color: var(--text-secondary); font-size: 0.95rem; max-width: 540px; margin: 0 auto; }

/* ── CONTENT ── */
.content { max-width: 780px; margin: 0 auto; padding: 40px 24px 80px; }

h2 {
  font-size: 1.4rem; font-weight: 700; color: var(--text-primary);
  margin: 42px 0 14px; padding-bottom: 10px;
  border-bottom: 1px solid var(--dark-border-bright);
  letter-spacing: -0.01em;
}
h2:first-child { margin-top: 0; }
h3 { font-size: 1.05rem; font-weight: 600; color: var(--text-primary); margin: 26px 0 10px; }
h4 { font-size: 0.72rem; font-weight: 700; letter-spacing: 0.1em; text-transform: uppercase; color: var(--text-secondary); margin: 18px 0 8px; }

p { margin-bottom: 14px; color: var(--text-secondary); font-size: 0.93rem; line-height: 1.8; }

/* Callouts */
.callout {
  border-radius: var(--radius); padding: 14px 16px; margin: 18px 0;
  display: flex; gap: 12px; align-items: flex-start; font-size: 0.87rem; line-height: 1.65;
  border: 1px solid;
}
.callout-icon { font-size: 1rem; flex-shrink: 0; margin-top: 2px; }
.callout p { margin: 0; color: inherit; font-size: inherit; }
.callout strong { display: block; margin-bottom: 3px; font-weight: 700; }
.callout.info { background: rgba(97,218,251,0.06); border-color: rgba(97,218,251,0.2); color: #9EEEFF; }
.callout.tip { background: rgba(74,222,128,0.06); border-color: rgba(74,222,128,0.2); color: #86EFAC; }
.callout.warning { background: rgba(251,191,36,0.06); border-color: rgba(251,191,36,0.2); color: #FDE68A; }
.callout.danger { background: rgba(248,113,113,0.06); border-color: rgba(248,113,113,0.2); color: #FCA5A5; }

/* Code */
pre {
  background: #0D1117; border: 1px solid var(--dark-border);
  border-radius: var(--radius); padding: 18px 20px;
  overflow-x: auto; font-size: 0.84rem; line-height: 1.7; margin: 14px 0;
  position: relative;
}
pre .lang-label {
  position: absolute; top: 8px; right: 12px;
  font-size: 0.6rem; font-weight: 700; letter-spacing: 0.12em;
  text-transform: uppercase; color: rgba(255,255,255,0.2);
}
code { font-family: 'SF Mono', 'Fira Code', Consolas, monospace; }
p code, li code, td code {
  background: rgba(97,218,251,0.08); color: var(--react-blue);
  padding: 2px 6px; border-radius: 4px; font-size: 0.85em;
}

/* Syntax */
.kw { color: #FF79C6; }
.ty { color: #8BE9FD; }
.st { color: #F1FA8C; }
.cm { color: #6272A4; }
.fn { color: #50FA7B; }
.nu { color: #BD93F9; }
.at { color: #FFB86C; }
.pr { color: #8BE9FD; }
.tag-c { color: #FF79C6; }   /* JSX tags */
.jsx-attr { color: #50FA7B; }  /* JSX attributes */
.imp { color: #FFB86C; }    /* imports */

/* Tables */
table {
  width: 100%; border-collapse: collapse; margin: 18px 0;
  font-size: 0.86rem; border-radius: var(--radius); overflow: hidden;
}
th {
  background: rgba(255,255,255,0.05); color: var(--text-secondary);
  font-weight: 600; padding: 10px 14px; text-align: left;
  font-size: 0.75rem; text-transform: uppercase; letter-spacing: 0.06em;
}
td { padding: 10px 14px; border-top: 1px solid var(--dark-border); color: var(--text-secondary); }

/* Def list */
.def-list { list-style: none; }
.def-list li {
  padding: 12px 0; border-bottom: 1px solid var(--dark-border);
  display: grid; grid-template-columns: 180px 1fr; gap: 16px; font-size: 0.88rem;
}
.def-list li:last-child { border-bottom: none; }
.def-term { font-weight: 600; color: var(--react-blue); font-family: 'SF Mono', monospace; font-size: 0.83rem; }
.def-desc { color: var(--text-secondary); }

/* Progress */
.progress { height: 3px; background: var(--dark-border); border-radius: 2px; margin-bottom: 30px; }
.progress-bar { height: 100%; background: linear-gradient(90deg, var(--react-blue), var(--ts-blue)); border-radius: 2px; }

/* Two col */
.two-col { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin: 14px 0; }
@media (max-width: 600px) { .two-col { grid-template-columns: 1fr; } .def-list li { grid-template-columns: 1fr; } }

/* Step list */
.step-list { list-style: none; counter-reset: steps; }
.step-list li {
  counter-increment: steps; padding: 12px 0 12px 48px; position: relative;
  border-bottom: 1px solid var(--dark-border); font-size: 0.9rem; color: var(--text-secondary);
}
.step-list li:last-child { border-bottom: none; }
.step-list li::before {
  content: counter(steps); position: absolute; left: 0; top: 12px;
  width: 28px; height: 28px; background: linear-gradient(135deg, var(--react-blue), var(--ts-blue));
  color: #000; border-radius: 50%; display: flex; align-items: center;
  justify-content: center; font-size: 0.72rem; font-weight: 800;
}

/* ul/ol */
.content ul, .content ol {
  padding-left: 22px; margin: 10px 0 14px;
  color: var(--text-secondary); font-size: 0.9rem; line-height: 1.85;
}

/* Chapter nav */
.chapter-nav { display: flex; gap: 12px; margin-top: 48px; padding-top: 22px; border-top: 1px solid var(--dark-border); }
.chapter-nav a {
  flex: 1; display: flex; flex-direction: column; gap: 4px; padding: 14px;
  background: var(--dark-card); border: 1px solid var(--dark-border);
  border-radius: var(--radius); text-decoration: none; color: inherit;
  transition: border-color 0.2s;
}
.chapter-nav a:hover { border-color: var(--dark-border-bright); }
.nav-dir { font-size: 0.7rem; color: var(--text-muted); text-transform: uppercase; letter-spacing: 0.1em; }
.nav-title-text { font-weight: 600; color: var(--react-blue); font-size: 0.88rem; }
.prev { text-align: left; } .next { text-align: right; }

/* Overview grid */
.overview-grid { display: grid; grid-template-columns: repeat(auto-fill, minmax(220px, 1fr)); gap: 12px; margin: 14px 0; }
.overview-card {
  background: var(--dark-bg); border: 1px solid var(--dark-border);
  border-radius: var(--radius); padding: 16px;
}
.overview-card .ov-icon { font-size: 1.5rem; margin-bottom: 8px; }
.overview-card h3 { font-size: 0.88rem; margin: 0 0 5px; }
.overview-card p { font-size: 0.78rem; margin: 0; color: var(--text-muted); line-height: 1.5; }

/* Site footer */
.site-footer {
  border-top: 1px solid var(--dark-border); padding: 28px 24px;
  text-align: center; font-size: 0.78rem; color: var(--text-muted);
}
.site-footer a { color: var(--react-blue); text-decoration: none; }

/* Inline tag */
.tag {
  display: inline-block; padding: 2px 8px; border-radius: 5px;
  font-size: 0.7rem; font-weight: 600; letter-spacing: 0.03em; margin-right: 5px;
}
.tag-react { background: rgba(97,218,251,0.12); color: var(--react-blue); border: 1px solid rgba(97,218,251,0.25); }
.tag-ts { background: rgba(49,120,198,0.15); color: #7AB3E0; border: 1px solid rgba(49,120,198,0.3); }
.tag-new { background: rgba(74,222,128,0.1); color: #4ADE80; border: 1px solid rgba(74,222,128,0.25); }
.tag-warn { background: rgba(251,191,36,0.1); color: #FBBF24; border: 1px solid rgba(251,191,36,0.25); }