:root {
  --font-display: 'Outfit', system-ui, sans-serif;
  --font-body: 'IBM Plex Sans', system-ui, sans-serif;
  --font-code: 'Fira Code', Consolas, monospace;

  --bg: #ffffff;
  --fg: #171717;
  --fg-muted: #6b7280;
  --fg-faint: #b0b6bf;
  --accent: #4f46e5;
  --accent-hover: #4338ca;
  --border: #f0f0f0;
  --code-bg: #f3f2ff;
  --sidebar-w: 240px;
  --content-max: 640px;
}

html[data-theme="dark"] {
  --bg: #161616;
  --fg: #e5e5e5;
  --fg-muted: #999;
  --fg-faint: #555;
  --accent: #a78bfa;
  --accent-hover: #c4b5fd;
  --border: #1e1e1e;
  --code-bg: #110f1a;
}

*, *::before, *::after { margin: 0; padding: 0; box-sizing: border-box; }
html { scroll-behavior: smooth; }

body {
  font-family: var(--font-body);
  background: var(--bg);
  color: var(--fg);
  line-height: 1.75;
  font-size: 1rem;
  display: flex;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
}

/* --- Sidebar --- */
.sidebar {
  width: var(--sidebar-w);
  min-width: var(--sidebar-w);
  background: radial-gradient(ellipse at top left, #f3f2ff 0%, var(--bg) 70%);
  position: fixed;
  top: 0; left: 0; bottom: 0;
  overflow-y: auto;
  z-index: 100;
  display: flex;
  flex-direction: column;
}

.sidebar-header {
  padding: 2.5rem 1.5rem 1.25rem;
}

.sidebar-top {
  display: flex;
  align-items: center;
}

.sidebar-logo {
  font-family: var(--font-display);
  font-size: 1rem;
  font-weight: 700;
  color: var(--fg);
  text-decoration: none;
  letter-spacing: -0.02em;
  transition: color 0.15s ease;
}

.sidebar-logo:hover { color: var(--accent); text-decoration: none; }

.logo-mark {
  display: inline-block;
  font-family: var(--font-code);
  letter-spacing: -0.2em;
  margin-left: -0.02em;
}

.title-logo-mark {
  margin-left: 0.05em;
  margin-right: 0.62em;
}

.theme-toggle {
  background: none;
  border: none;
  cursor: pointer;
  color: var(--fg-faint);
  padding: 0.25rem;
  display: flex;
  align-items: center;
  transition: color 0.15s ease;
}

.theme-toggle:hover { color: var(--fg); }
.theme-toggle svg { width: 15px; height: 15px; }

html[data-theme="light"] .icon-sun { display: none; }
html[data-theme="dark"] .icon-moon { display: none; }
html[data-theme="dark"] .sidebar { background: radial-gradient(ellipse at top left, #100f18 0%, var(--bg) 70%); }

.sidebar-links { padding: 0; flex: 1; }

.sidebar-links a {
  display: flex;
  align-items: baseline;
  gap: 0.2rem;
  padding: 0.3rem 1.5rem;
  font-family: var(--font-body);
  font-size: 0.8rem;
  color: var(--fg-muted);
  text-decoration: none;
  line-height: 1.6;
  transition: color 0.15s ease;
}

.sidebar-links a:hover {
  color: var(--fg);
  text-decoration: none;
}

.sidebar-links a.active {
  color: var(--accent);
  font-weight: 500;
}

.ch-num {
  font-family: var(--font-body);
  font-size: 0.8rem;
  font-weight: 400;
  color: var(--fg-faint);
}

.sidebar-links a.active .ch-num { color: var(--accent); }

.sidebar-about { margin-top: 0.5rem; }

.sidebar-footer {
  padding: 1rem 1.5rem;
}

/* --- Mobile menu --- */
.mobile-menu-btn {
  display: none;
  position: fixed;
  top: 0.75rem;
  left: 0.75rem;
  z-index: 200;
  background: var(--bg);
  border: 1px solid var(--border);
  border-radius: 8px;
  width: 2.25rem;
  height: 2.25rem;
  cursor: pointer;
  color: var(--fg-muted);
  font-size: 0;
  align-items: center;
  justify-content: center;
}

.mobile-menu-btn svg { width: 16px; height: 16px; }

.mobile-overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,0.2);
  z-index: 50;
  opacity: 0;
  transition: opacity 0.25s ease;
}

/* --- Content --- */
.content {
  margin-left: var(--sidebar-w);
  flex: 1;
  padding: 2.5rem 4rem;
  max-width: calc(var(--content-max) + 8rem);
  animation: fadeIn 0.3s ease;
}

@keyframes fadeIn {
  from { opacity: 0; }
  to { opacity: 1; }
}

/* --- Typography --- */
h1 {
  font-family: var(--font-display);
  font-size: 1.75rem;
  font-weight: 800;
  line-height: 1.25;
  margin: 0 0 2rem;
  letter-spacing: -0.04em;
}

h2 {
  font-family: var(--font-display);
  font-size: 1.15rem;
  font-weight: 700;
  line-height: 1.3;
  margin: 3.5rem 0 1rem;
  letter-spacing: -0.025em;
}

h3 {
  font-family: var(--font-display);
  font-size: 0.95rem;
  font-weight: 700;
  line-height: 1.4;
  margin: 2.5rem 0 0.75rem;
  letter-spacing: -0.01em;
}

p { margin: 1rem 0; }

a {
  color: var(--accent);
  text-decoration: none;
  transition: color 0.15s ease;
}

a:hover {
  color: var(--accent-hover);
  text-decoration: underline;
  text-underline-offset: 2px;
  text-decoration-thickness: 1px;
}

strong { font-weight: 600; }

/* --- Code & Diagrams --- */
code {
  font-family: var(--font-code);
  font-size: 0.85em;
  background: var(--code-bg);
  padding: 0.15em 0.35em;
  border-radius: 4px;
}

pre {
  background: var(--code-bg);
  border-radius: 6px;
  padding: 1.25rem 1.5rem;
  overflow-x: auto;
  margin: 1.75rem 0;
  line-height: 1.45;
}

pre code {
  background: none;
  padding: 0;
  font-size: 0.85rem;
  line-height: inherit;
  display: block;
}

.dc { color: #7c7cf0; }
html[data-theme="dark"] .dc { color: #6e6ec0; }

/* --- Blockquotes --- */
blockquote {
  border-left: 2px solid var(--border);
  padding-left: 1.25rem;
  margin: 1.5rem 0;
  color: var(--fg-muted);
}

blockquote p { margin: 0.5rem 0; }

/* --- Tables --- */
table {
  width: 100%;
  border-collapse: collapse;
  margin: 1.5rem 0;
  font-size: 0.88rem;
}

th, td {
  text-align: left;
  padding: 0.6rem 0.75rem;
  border-bottom: 1px solid var(--border);
}

th {
  font-family: var(--font-display);
  font-weight: 600;
  font-size: 0.7rem;
  text-transform: uppercase;
  letter-spacing: 0.06em;
  color: var(--fg-muted);
}

tr:last-child td { border-bottom: none; }

/* --- Lists --- */
ul, ol { margin: 1rem 0; padding-left: 1.5rem; }
li { margin: 0.35rem 0; }
li::marker { color: var(--fg-faint); }

/* --- Misc --- */
hr { border: none; border-top: 1px solid var(--border); margin: 3rem 0; }
img { max-width: 100%; height: auto; margin: 1.5rem 0; }

/* --- Prev/Next --- */
.prev-next {
  display: flex;
  justify-content: space-between;
  margin-top: 5rem;
  padding-top: 2rem;
  border-top: 1px solid var(--border);
  font-family: var(--font-display);
  font-size: 0.88rem;
}

.prev-next a {
  max-width: 48%;
  color: var(--fg-muted);
  font-weight: 500;
  padding: 0.5rem 0.75rem;
  border-radius: 6px;
  transition: all 0.15s ease;
}

.prev-next a:hover { color: var(--accent); background: var(--code-bg); text-decoration: none; }

.license {
  margin-top: 3rem;
  font-size: 0.75rem;
  color: var(--fg-faint);
  text-align: center;
}

/* --- Scrollbar --- */
::-webkit-scrollbar { width: 0px; }
::selection { background: var(--accent); color: #fff; }

/* --- Mobile --- */
@media (max-width: 860px) {
  .mobile-menu-btn { display: flex; }
  .mobile-overlay { display: block; }

  .sidebar {
    transform: translateX(-100%);
    transition: transform 0.25s cubic-bezier(0.4, 0, 0.2, 1);
    background: var(--bg);
  }

  .sidebar.open {
    transform: translateX(0);
    box-shadow: 2px 0 24px rgba(0,0,0,0.06);
  }

  .mobile-overlay.open { opacity: 1; }

  .content {
    margin-left: 0;
    padding: 2rem 1.5rem;
    padding-top: 4rem;
    max-width: 100%;
  }

  h1 { font-size: 1.5rem; }
}

@media print {
  .sidebar, .mobile-menu-btn, .prev-next, .mobile-overlay { display: none !important; }
  .content { margin-left: 0; max-width: 100%; padding: 0; }
}