* {
  margin: 0;
  padding: 0;
  box-sizing: border-box;
}

html {
  scroll-behavior: smooth;
}

/* ---------- THEME VARIABLES ---------- */
:root {
  --bg: #f9f9f9;
  --text: #222;
  --card: #fff;
  --border: #ddd;
  --link: #007bff;
}

[data-theme="dark"] {
  --bg: #0f1116;
  --text: #ddd;
  --card: #181b22;
  --border: #333;
  --link: #4da3ff;
}

body {
  font-family: sans-serif;
  line-height: 1.6;
  background: var(--bg);
  color: var(--text);
  transition: background 0.3s, color 0.3s;
}

header {
  background: var(--card);
  padding: 10px 20px;
  border-bottom: 1px solid var(--border);
  display: flex;
  justify-content: space-between;
  align-items: center;
  position: sticky;
  top: 0;
  z-index: 100;
}

.header-controls {
  display: flex;
  align-items: center;
  gap: 10px;
}

#theme-toggle {
  background: none;
  border: 1px solid var(--border);
  border-radius: 6px;
  padding: 4px 8px;
  color: var(--text);
  cursor: pointer;
  transition: background 0.2s;
}

#theme-toggle:hover {
  background: var(--border);
}

.layout {
  display: grid;
  grid-template-columns: 220px 1fr 200px;
  min-height: calc(100vh - 60px);
}

.sidebar {
  background: var(--card);
  border-right: 1px solid var(--border);
  padding: 20px;
  transition: background 0.3s;
}

.sidebar h2 {
  cursor: pointer;
  font-size: 1.1rem;
  margin: 15px 0 5px;
}

.sidebar ul {
  list-style: none;
  margin: 0 0 10px;
  padding-left: 10px;
  transition: all 0.3s ease;
}

.sidebar ul.collapsed {
  max-height: 0;
  overflow: hidden;
  opacity: 0;
}

.sidebar h2::before {
  content: "▸";
  margin-right: 6px;
  transition: transform 0.2s;
}

.sidebar h2.open::before {
  transform: rotate(90deg);
}

.sidebar a {
  color: var(--text);
  text-decoration: none;
  display: block;
  padding: 4px 0;
}

.sidebar a:hover {
  color: var(--link);
}

.sidebar a.active {
  color: var(--link);
  font-weight: bold;
}

main {
  padding: 20px 40px;
}

main section {
  margin-bottom: 40px;
}

.toc {
  background: var(--card);
  border-left: 1px solid var(--border);
  padding: 20px;
  position: sticky;
  top: 60px;
  height: calc(100vh - 60px);
  overflow-y: auto;
  transition: background 0.3s;
}

.toc ul {
  list-style: none;
}

.toc a {
  text-decoration: none;
  color: var(--text);
}

.toc a:hover {
  color: var(--link);
}

.nitro {
  display: inline-block;
  margin-left: 6px;
  padding: 2px 6px;
  font-size: 0.75em;
  font-weight: 600;
  color: #fff;
  background: linear-gradient(90deg, #5865F2 0%, #EB459E 100%);
  border-radius: 6px;
  text-transform: uppercase;
  letter-spacing: 0.5px;
  vertical-align: middle;
}

/* Mobile responsive */
@media (max-width: 900px) {
  .layout {
    grid-template-columns: 1fr;
  }
  .sidebar {
    border-right: none;
    border-bottom: 1px solid var(--border);
    padding: 10px 20px;
  }
  .toc {
    display: none;
  }
}