:root {
  --bg: #fff;
  --bg2: #f9fafb;
  --accent: #1d4ed8;
  --accent-light: #eff6ff;
  --text: #111827;
  --sub: #6b7280;
  --border: #e5e7eb;
  --sidebar: 220px;
}

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

body {
  font-family: -apple-system, BlinkMacSystemFont, 'Segoe UI', system-ui, sans-serif;
  font-size: 14px;
  line-height: 1.65;
  color: var(--text);
  background: var(--bg);
}

/* sidebar */
.sidebar {
  position: fixed;
  top: 0; left: 0; bottom: 0;
  width: var(--sidebar);
  background: var(--bg2);
  border-right: 1px solid var(--border);
  overflow-y: auto;
  z-index: 100;
}

.sidebar-header {
  padding: 16px 14px 12px;
  border-bottom: 1px solid var(--border);
}

.sidebar-header .label {
  font-size: 10px;
  font-weight: 700;
  letter-spacing: .8px;
  text-transform: uppercase;
  color: var(--sub);
  margin-bottom: 2px;
}

.sidebar-header .name {
  font-size: 13px;
  font-weight: 600;
  color: var(--text);
}

.sidebar-nav {
  padding: 8px;
}

.nav-group {
  font-size: 10px;
  font-weight: 700;
  letter-spacing: .7px;
  text-transform: uppercase;
  color: var(--sub);
  padding: 8px 6px 3px;
}

.sidebar-nav a {
  display: flex;
  align-items: center;
  gap: 7px;
  padding: 5px 6px;
  font-size: 13px;
  color: var(--text);
  text-decoration: none;
  border-radius: 4px;
  border-left: 2px solid transparent;
  margin-bottom: 1px;
  transition: background .1s;
}

.sidebar-nav a:hover { background: #f3f4f6; }

.sidebar-nav a.active {
  background: var(--accent-light);
  color: var(--accent);
  border-left-color: var(--accent);
  font-weight: 500;
}

.n { font-size: 10px; font-weight: 700; color: var(--sub); min-width: 13px; }
.sidebar-nav a.active .n { color: var(--accent); }

/* overlay */
.overlay {
  display: none;
  position: fixed;
  inset: 0;
  background: rgba(0,0,0,.25);
  z-index: 99;
}
.overlay.show { display: block; }

/* topbar */
.topbar {
  position: sticky;
  top: 0;
  background: var(--bg);
  border-bottom: 1px solid var(--border);
  height: 44px;
  display: flex;
  align-items: center;
  padding: 0 24px;
  z-index: 50;
}

.menu-btn {
  display: none;
  background: none;
  border: none;
  cursor: pointer;
  color: var(--text);
  padding: 4px;
  margin-right: 8px;
}

.breadcrumb {
  font-size: 13px;
  color: var(--sub);
  display: flex;
  align-items: center;
  gap: 6px;
}

.breadcrumb a { color: var(--accent); text-decoration: none; }
.breadcrumb a:hover { text-decoration: underline; }
.sep { color: var(--border); }

/* layout */
.layout { margin-left: var(--sidebar); }

.content {
  max-width: 780px;
  padding: 36px 36px 80px;
}

/* page title */
.page-title {
  margin-bottom: 28px;
  padding-bottom: 18px;
  border-bottom: 1px solid var(--border);
}

.topic-tag {
  font-size: 11px;
  font-weight: 600;
  color: var(--sub);
  text-transform: uppercase;
  letter-spacing: .6px;
  margin-bottom: 6px;
}

.page-title h1 {
  font-size: 22px;
  font-weight: 700;
  color: var(--text);
  line-height: 1.2;
  margin-bottom: 6px;
}

.page-title p {
  font-size: 13.5px;
  color: var(--sub);
}

/* section headings */
h2 {
  font-size: 15px;
  font-weight: 700;
  color: var(--text);
  margin: 28px 0 10px;
  padding-bottom: 7px;
  border-bottom: 1px solid var(--border);
}

h3 {
  font-size: 13.5px;
  font-weight: 600;
  color: var(--text);
  margin: 18px 0 7px;
}

h4 {
  font-size: 11px;
  font-weight: 700;
  color: var(--sub);
  text-transform: uppercase;
  letter-spacing: .5px;
  margin: 14px 0 5px;
}

/* prose */
p { margin-bottom: 10px; font-size: 13.5px; }
p:last-child { margin-bottom: 0; }

ul, ol { padding-left: 18px; margin: 6px 0 10px; }
li { font-size: 13.5px; margin-bottom: 3px; }

strong { font-weight: 600; }

/* note blocks */
.note {
  border-left: 3px solid var(--border);
  padding: 8px 12px;
  margin: 10px 0;
  font-size: 13.5px;
  color: #374151;
  font-style: italic;
  background: var(--bg2);
}

.note.blue  { border-color: var(--accent); background: var(--accent-light); color: #1e3a8a; font-style: normal; }
.note.red   { border-color: #dc2626; background: #fef2f2; color: #7f1d1d; font-style: normal; }
.note.green { border-color: #16a34a; background: #f0fdf4; color: #14532d; font-style: normal; }
.note.amber { border-color: #d97706; background: #fffbeb; color: #78350f; font-style: normal; }

.note-label {
  font-size: 10px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .6px;
  opacity: .7;
  margin-bottom: 4px;
}

/* table */
.table-wrap { overflow-x: auto; margin: 10px 0; }

table { width: 100%; border-collapse: collapse; font-size: 13px; }

th {
  text-align: left;
  padding: 7px 10px;
  font-size: 10px;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: .4px;
  color: var(--sub);
  background: var(--bg2);
  border-bottom: 1px solid var(--border);
  border-top: 1px solid var(--border);
}

td {
  padding: 7px 10px;
  border-bottom: 1px solid var(--border);
  vertical-align: top;
}

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

/* collapsible Q&A */
.qa {
  border: 1px solid var(--border);
  border-radius: 5px;
  margin-bottom: 8px;
  overflow: hidden;
}

.qa-q {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 12px;
  padding: 10px 12px;
  cursor: pointer;
  background: var(--bg);
  user-select: none;
  font-size: 13.5px;
  font-weight: 500;
}

.qa-q:hover { background: var(--bg2); }

.qa-q .mark {
  font-size: 11px;
  font-weight: 600;
  color: var(--sub);
  white-space: nowrap;
  flex-shrink: 0;
  margin-top: 1px;
}

.qa-q .arrow {
  font-size: 9px;
  color: var(--sub);
  transition: transform .18s;
  flex-shrink: 0;
  margin-top: 3px;
}

.qa.open .qa-q { background: var(--bg2); }
.qa.open .qa-q .arrow { transform: rotate(90deg); }

.qa-a {
  display: none;
  padding: 12px 14px;
  border-top: 1px solid var(--border);
  background: var(--bg);
  font-size: 13.5px;
}

.qa.open .qa-a { display: block; }

.qa-a p { margin-bottom: 8px; }
.qa-a p:last-child { margin-bottom: 0; }

/* grid */
.grid2 { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; }

/* prev/next */
.page-nav {
  display: flex;
  gap: 8px;
  margin-top: 40px;
  padding-top: 18px;
  border-top: 1px solid var(--border);
}

.page-nav a {
  font-size: 13px;
  color: var(--accent);
  text-decoration: none;
  border: 1px solid var(--border);
  padding: 6px 12px;
  border-radius: 4px;
  transition: border-color .1s;
}

.page-nav a:hover { border-color: var(--accent); }

/* scrollbar */
::-webkit-scrollbar { width: 5px; }
::-webkit-scrollbar-track { background: var(--bg2); }
::-webkit-scrollbar-thumb { background: var(--border); border-radius: 3px; }

/* print */
@media print {
  .sidebar, .topbar { display: none !important; }
  .layout { margin: 0; }
  .content { padding: 0; max-width: 100%; }
}

/* mobile */
@media (max-width: 860px) {
  .sidebar { transform: translateX(-100%); transition: transform .22s; }
  .sidebar.open { transform: none; }
  .layout { margin-left: 0; }
  .menu-btn { display: flex; }
  .content { padding: 20px 16px 60px; }
  .grid2 { grid-template-columns: 1fr; }
}