:root {
  --bg: #ffffff;
  --bg-alt: #f5f6f8;
  --text: #1c2127;
  --text-muted: #5b6472;
  --border: #e2e5ea;
  --accent: #1a73e8;
  --code-bg: #0d1117;
  --sidebar-w: 320px;
}

@media (prefers-color-scheme: dark) {
  :root {
    --bg: #14171c;
    --bg-alt: #1b1f26;
    --text: #e6e9ee;
    --text-muted: #9aa4b2;
    --border: #2b3038;
    --accent: #6cabff;
    --code-bg: #0d1117;
  }
}

* { box-sizing: border-box; }

body {
  margin: 0;
  font-family: "Segoe UI", -apple-system, BlinkMacSystemFont, Roboto, Helvetica, Arial, sans-serif;
  background: var(--bg);
  color: var(--text);
  line-height: 1.65;
}

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

.sidebar {
  position: fixed;
  top: 0; left: 0; bottom: 0;
  width: var(--sidebar-w);
  overflow-y: auto;
  background: var(--bg-alt);
  border-right: 1px solid var(--border);
  padding: 1rem 0 3rem;
}

.sidebar-title {
  font-weight: 700;
  font-size: 1.05rem;
  padding: 0 1.25rem 1rem;
  border-bottom: 1px solid var(--border);
  margin-bottom: 0.5rem;
}

.sidebar-part { padding: 0.4rem 1.25rem; }
.sidebar-part-title {
  font-size: 0.78rem;
  text-transform: uppercase;
  letter-spacing: 0.04em;
  color: var(--text-muted);
  margin: 0.6rem 0 0.35rem;
}
.sidebar-part ul { list-style: none; margin: 0; padding: 0; }
.sidebar-part li { margin: 0.15rem 0; }
.sidebar-part li a {
  display: block;
  color: var(--text);
  font-size: 0.9rem;
  padding: 0.25rem 0.5rem;
  border-radius: 6px;
}
.sidebar-part li a:hover { background: var(--border); text-decoration: none; }
.sidebar-part li.active a { background: var(--accent); color: #fff; }
.sidebar-part li.planned a { color: var(--text-muted); font-style: italic; }

.nav-toggle {
  display: none;
  position: fixed;
  top: 0.75rem; left: 0.75rem;
  z-index: 20;
  width: 2.25rem; height: 2.25rem;
  border-radius: 6px;
  border: 1px solid var(--border);
  background: var(--bg-alt);
  color: var(--text);
  font-size: 1.1rem;
  cursor: pointer;
}

.content {
  margin-left: var(--sidebar-w);
  padding: 2.5rem 3rem 4rem;
  max-width: 860px;
}

article h1 { font-size: 1.9rem; margin-top: 0; }
article h2 { font-size: 1.4rem; margin-top: 2.2rem; border-top: 1px solid var(--border); padding-top: 1.5rem; }
article h3 { font-size: 1.15rem; margin-top: 1.6rem; }
.subtitle { color: var(--text-muted); margin-top: -0.5rem; }
.tbd { color: var(--text-muted); font-style: italic; }
.badge {
  font-size: 0.7rem;
  color: var(--text-muted);
  border: 1px solid var(--border);
  border-radius: 999px;
  padding: 0.05rem 0.5rem;
}

pre:not(.mermaid) {
  background: var(--code-bg);
  border-radius: 8px;
  padding: 1rem 1.1rem;
  overflow-x: auto;
}
code { font-family: "Cascadia Code", Consolas, "SF Mono", monospace; font-size: 0.88rem; }
:not(pre) > code {
  background: var(--bg-alt);
  border: 1px solid var(--border);
  border-radius: 4px;
  padding: 0.08rem 0.35rem;
}

blockquote {
  margin: 1rem 0;
  padding: 0.5rem 1rem;
  border-left: 3px solid var(--accent);
  background: var(--bg-alt);
  color: var(--text-muted);
}

table { border-collapse: collapse; width: 100%; margin: 1rem 0; }
th, td { border: 1px solid var(--border); padding: 0.5rem 0.7rem; text-align: left; }
th { background: var(--bg-alt); }

.mermaid-wrap {
  position: relative;
  width: 100%;
  height: 420px;
  border: 1px solid var(--border);
  border-radius: 8px;
  background: #fff;
  margin: 1.25rem 0;
  overflow: hidden;
}
.mermaid-wrap svg { display: block; max-width: none; }
.mermaid-wrap::after {
  content: "Kéo để di chuyển · cuộn hoặc dùng nút +/- để zoom";
  position: absolute;
  bottom: 6px; right: 10px;
  font-size: 0.7rem;
  color: #8a919c;
  pointer-events: none;
}

.prev-next {
  display: flex;
  justify-content: space-between;
  gap: 1rem;
  margin-top: 3rem;
  padding-top: 1.5rem;
  border-top: 1px solid var(--border);
  font-size: 0.92rem;
}
.prev-next a { max-width: 46%; }
.prev-next .next { text-align: right; margin-left: auto; }

@media (max-width: 900px) {
  .nav-toggle { display: block; }
  .sidebar {
    transform: translateX(-100%);
    transition: transform 0.2s ease;
    z-index: 15;
    box-shadow: 2px 0 12px rgba(0,0,0,0.25);
  }
  .sidebar.open { transform: translateX(0); }
  .content { margin-left: 0; padding: 4rem 1.25rem 3rem; }
}