:root {
  --bg: #faf8f3; --bg-alt: #ffffff; --bg-soft: #f3efe6;
  --text: #2b2b2b; --muted: #6b6b6b;
  --primary: #5b4b8a; --primary-dark: #433569; --primary-light: #ede9f5;
  --accent: #d97757; --accent-light: #fde8dc;
  --green: #5e8b5e; --green-light: #e0f0dc;
  --blue: #4a7ba6; --blue-light: #dce9f5;
  --yellow: #c9a227; --yellow-light: #fff0cc;
  --pink: #c77b9e; --pink-light: #f5e0ea;
  --border: #e5e1d8; --shadow: 0 2px 12px rgba(0,0,0,0.05);
}
[data-theme="dark"] {
  --bg: #1a1a1d; --bg-alt: #242428; --bg-soft: #2d2d32;
  --text: #eceae4; --muted: #9a968c;
  --primary: #a694d6; --primary-dark: #8c79c2; --primary-light: #2e2840;
  --accent: #e89376; --accent-light: #3a2a24;
  --green: #8bc48b; --green-light: #2a3a2a;
  --blue: #7ab5e0; --blue-light: #1f2e3a;
  --yellow: #e0c250; --yellow-light: #3a3120;
  --pink: #d9a0bd; --pink-light: #3a2830;
  --border: #36363b; --shadow: 0 2px 12px rgba(0,0,0,0.3);
}
* { box-sizing: border-box; margin: 0; padding: 0; }
html { scroll-behavior: smooth; }
body {
  font-family: -apple-system, 'Segoe UI', 'Malgun Gothic', 'Apple SD Gothic Neo', sans-serif;
  background: var(--bg); color: var(--text);
  line-height: 1.75; display: flex; min-height: 100vh;
}
aside {
  width: 290px; background: var(--bg-alt);
  border-right: 1px solid var(--border);
  position: sticky; top: 0; height: 100vh;
  overflow-y: auto; padding: 24px 20px; flex-shrink: 0;
}
aside h1 { font-size: 20px; margin-bottom: 2px; }
aside h1 a { color: var(--primary); text-decoration: none; }
aside h1 a:hover { color: var(--primary-dark); }
aside .sub { font-size: 11px; color: var(--muted); margin-bottom: 18px; letter-spacing: 1px; }
aside nav ol { list-style: none; }
aside nav > ol > li { margin-bottom: 4px; }
aside nav a {
  display: block; padding: 7px 12px;
  color: var(--text); text-decoration: none;
  font-size: 13.5px; border-radius: 6px;
  transition: all 0.15s;
}
aside nav a:hover { background: var(--primary-light); color: var(--primary); }
aside nav a.chap { font-weight: 600; }
aside nav a.active {
  background: var(--primary); color: #fff;
}
aside nav a.active:hover { background: var(--primary-dark); color: #fff; }
#theme-btn {
  width: 100%; margin-top: 16px; padding: 9px;
  background: var(--primary-light); color: var(--primary);
  border: 1px solid var(--border); border-radius: 6px;
  cursor: pointer; font-size: 12.5px; font-weight: 600;
  font-family: inherit;
}
#theme-btn:hover { background: var(--primary); color: #fff; }
#sidebar-toggle {
  display: none;
  position: fixed;
  top: 14px; left: 14px;
  z-index: 1001;
  width: 44px; height: 44px;
  background: var(--primary);
  color: #fff;
  border: none;
  border-radius: 8px;
  cursor: pointer;
  font-size: 20px;
  box-shadow: var(--shadow);
}
main { flex: 1; padding: 50px 60px; max-width: 960px; }
.progress-bar {
  background: var(--bg-soft);
  border: 1px solid var(--border);
  border-radius: 20px;
  height: 8px;
  margin-bottom: 24px;
  overflow: hidden;
  position: relative;
}
.progress-bar .fill {
  background: linear-gradient(90deg, var(--primary) 0%, var(--accent) 100%);
  height: 100%;
  border-radius: 20px;
  transition: width 0.4s ease;
}
.progress-label {
  font-size: 11px;
  color: var(--muted);
  margin-bottom: 6px;
  letter-spacing: 1px;
  font-weight: 600;
}
.page-nav {
  margin-bottom: 24px;
}
.page-nav a {
  color: var(--muted); text-decoration: none;
  font-size: 13px; padding: 6px 12px;
  border: 1px solid var(--border); border-radius: 6px;
  display: inline-block;
}
.page-nav a:hover { color: var(--primary); border-color: var(--primary); }
.page-nav-bottom {
  display: flex; justify-content: space-between;
  margin: 40px 0 20px;
}
.page-nav-bottom a {
  color: var(--primary); text-decoration: none;
  font-size: 14px; padding: 12px 20px;
  background: var(--bg-alt); border: 1px solid var(--border);
  border-radius: 8px; font-weight: 600;
  transition: all 0.15s;
}
.page-nav-bottom a:hover {
  background: var(--primary); color: #fff; border-color: var(--primary);
}
.page-nav-bottom .spacer { flex: 1; }
.hero {
  background: linear-gradient(135deg, #5b4b8a 0%, #d97757 100%);
  color: #fff; padding: 50px 42px;
  border-radius: 14px; margin-bottom: 40px;
}
.hero h2 { font-size: 32px; margin-bottom: 10px; letter-spacing: -0.5px; }
.hero p { font-size: 15px; opacity: 0.95; max-width: 640px; margin-bottom: 16px; }
.hero .tags span {
  display: inline-block; background: rgba(255,255,255,0.2);
  padding: 5px 13px; border-radius: 20px;
  font-size: 12px; margin-right: 6px; margin-top: 4px;
}
.toc-grid {
  display: grid; grid-template-columns: repeat(auto-fit, minmax(240px, 1fr));
  gap: 14px; margin: 24px 0;
}
.toc-card {
  background: var(--bg-alt); border: 1px solid var(--border);
  border-radius: 10px; padding: 20px;
  text-decoration: none; color: var(--text);
  transition: all 0.2s;
  display: block;
}
.toc-card:hover {
  transform: translateY(-3px);
  border-color: var(--primary);
  box-shadow: var(--shadow);
}
.toc-card .num {
  font-size: 11px; font-weight: 700;
  color: var(--accent); letter-spacing: 2px;
}
.toc-card h3 {
  font-size: 17px; color: var(--primary);
  margin: 6px 0 4px; border: none; padding: 0;
}
.toc-card p {
  font-size: 12.5px; color: var(--muted);
  margin: 0;
}
section.chapter {
  background: var(--bg-alt); border: 1px solid var(--border);
  border-radius: 12px; padding: 40px 44px;
  margin-bottom: 32px; box-shadow: var(--shadow);
}
.chap-num {
  display: inline-block; font-size: 11px; font-weight: 700;
  color: var(--accent); letter-spacing: 2.5px; margin-bottom: 8px;
}
section.chapter > h2 {
  font-size: 28px; color: var(--primary);
  letter-spacing: -0.5px; margin-bottom: 4px;
}
section.chapter > .en {
  font-size: 13px; color: var(--muted);
  font-style: italic; margin-bottom: 24px;
}
section.chapter h3 {
  font-size: 19px; margin: 34px 0 12px;
  padding-left: 12px; border-left: 4px solid var(--accent);
}
section.chapter h4 {
  font-size: 15px; margin: 18px 0 8px;
  color: var(--primary); font-weight: 700;
}
section.chapter p { margin-bottom: 12px; }
section.chapter ul, section.chapter ol { margin: 10px 0 16px 22px; }
section.chapter li { margin-bottom: 6px; }
section.chapter strong { color: var(--primary); }
.term, .example, .tip, .warn, .quote {
  padding: 14px 18px; border-radius: 8px;
  margin: 16px 0; font-size: 14px; line-height: 1.7;
}
.term { background: var(--primary-light); border-left: 4px solid var(--primary); }
.term .word { display: block; font-weight: 700; color: var(--primary); font-size: 15px; margin-bottom: 4px; }
.example { background: var(--yellow-light); border-left: 4px solid var(--yellow); }
.example .label { display: block; font-size: 11px; font-weight: 700; color: var(--yellow); letter-spacing: 1.5px; margin-bottom: 6px; }
.tip { background: var(--green-light); border-left: 4px solid var(--green); }
.tip .label { display: block; font-size: 11px; font-weight: 700; color: var(--green); letter-spacing: 1.5px; margin-bottom: 6px; }
.warn { background: var(--accent-light); border-left: 4px solid var(--accent); }
.warn .label { display: block; font-size: 11px; font-weight: 700; color: var(--accent); letter-spacing: 1.5px; margin-bottom: 6px; }
.quote { background: var(--bg-soft); border-left: 4px solid var(--muted); font-style: italic; }
figure.figure {
  background: var(--bg-soft); border: 1px solid var(--border);
  border-radius: 10px; padding: 24px;
  margin: 24px 0; text-align: center;
}
figure.figure svg { max-width: 100%; height: auto; }
figure.figure figcaption {
  margin-top: 12px; font-size: 12.5px;
  color: var(--muted); font-style: italic;
}
svg text { font-family: -apple-system, 'Segoe UI', 'Malgun Gothic', sans-serif; }
.steps { counter-reset: step; margin: 20px 0; }
.step {
  position: relative; padding: 12px 18px 12px 52px;
  background: var(--bg-soft); border-radius: 8px;
  margin-bottom: 10px; counter-increment: step; font-size: 14px;
}
.step::before {
  content: counter(step);
  position: absolute; left: 14px; top: 50%;
  transform: translateY(-50%);
  width: 28px; height: 28px;
  background: var(--primary); color: #fff;
  border-radius: 50%;
  display: flex; align-items: center; justify-content: center;
  font-weight: 700; font-size: 13px;
}
table.compare {
  width: 100%; border-collapse: collapse;
  margin: 18px 0; font-size: 13.5px;
}
table.compare th, table.compare td {
  padding: 10px 12px; border: 1px solid var(--border);
  text-align: left; vertical-align: top;
}
table.compare th { background: var(--primary-light); color: var(--primary); font-weight: 700; }
table.compare tr:nth-child(even) td { background: var(--bg-soft); }
.two-col {
  display: grid; grid-template-columns: 1fr 1fr;
  gap: 14px; margin: 16px 0;
}
.col-box {
  background: var(--bg-soft); border: 1px solid var(--border);
  border-radius: 8px; padding: 16px;
}
.col-box h4 { margin-top: 0; }
.quiz-item {
  background: var(--bg-soft); border: 1px solid var(--border);
  border-radius: 8px; padding: 18px; margin-bottom: 14px;
}
.quiz-item .q { font-weight: 600; margin-bottom: 10px; }
.quiz-item button {
  display: block; width: 100%; text-align: left;
  padding: 10px 14px; margin: 5px 0;
  background: var(--bg-alt); border: 1px solid var(--border);
  border-radius: 6px; cursor: pointer; color: var(--text);
  font-size: 14px; font-family: inherit;
}
.quiz-item button:hover { border-color: var(--primary); }
.quiz-item button.correct { background: #c8e6c9; border-color: #4caf50; color: #1b5e20; }
.quiz-item button.wrong { background: #ffcdd2; border-color: #e53935; color: #b71c1c; }
footer {
  text-align: center; padding: 30px;
  color: var(--muted); font-size: 12px;
  border-top: 1px solid var(--border); margin-top: 40px;
}
@media (max-width: 900px) {
  body { flex-direction: column; }
  #sidebar-toggle { display: flex; align-items: center; justify-content: center; }
  aside {
    width: 280px;
    position: fixed;
    top: 0; left: 0;
    height: 100vh;
    z-index: 1000;
    transform: translateX(-100%);
    transition: transform 0.25s ease;
    box-shadow: var(--shadow);
  }
  aside.open { transform: translateX(0); }
  .sidebar-backdrop {
    display: none;
    position: fixed;
    inset: 0;
    background: rgba(0,0,0,0.4);
    z-index: 999;
  }
  .sidebar-backdrop.open { display: block; }
  main {
    padding: 70px 20px 30px;
    max-width: 100%;
  }
  section.chapter { padding: 24px; }
  .two-col { grid-template-columns: 1fr; }
  .hero { padding: 30px 24px; }
  .hero h2 { font-size: 26px; }
  .page-nav-bottom { flex-direction: column; gap: 8px; }
  .page-nav-bottom a { text-align: center; }
}