/* ============================================================
   Khóa học System Design (theo karanpratapsingh/system-design)
   Stylesheet dùng chung
   ============================================================ */

:root {
  --bg: #08110f;
  --bg-soft: #0d1a18;
  --bg-card: #11201d;
  --bg-code: #0a1513;
  --border: #1f332f;
  --border-soft: #182824;
  --text: #e6f0ee;
  --text-dim: #9db5b0;
  --text-faint: #6a807b;
  --accent: #14b8a6;
  --accent-2: #2dd4bf;
  --basic: #22c55e;
  --inter: #f59e0b;
  --adv: #ef4444;
  --radius: 12px;
  --mono: "JetBrains Mono", "Fira Code", "SF Mono", Consolas, "Liberation Mono", Menlo, monospace;
  --sans: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, "Helvetica Neue", Arial, "Noto Sans", sans-serif;
  --sidebar-w: 300px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; scroll-padding-top: 24px; }

body {
  margin: 0;
  font-family: var(--sans);
  background: var(--bg);
  color: var(--text);
  line-height: 1.7;
  font-size: 16px;
  -webkit-font-smoothing: antialiased;
}

a { color: var(--accent-2); text-decoration: none; }
a:hover { text-decoration: underline; }

/* ---------- Layout ---------- */
.layout { display: flex; min-height: 100vh; }

.sidebar {
  width: var(--sidebar-w);
  flex-shrink: 0;
  background: var(--bg-soft);
  border-right: 1px solid var(--border);
  position: fixed;
  top: 0; left: 0; bottom: 0;
  overflow-y: auto;
  padding: 0 0 40px;
  z-index: 40;
}

.sidebar-header {
  padding: 20px 22px 16px;
  position: sticky; top: 0;
  background: var(--bg-soft);
  border-bottom: 1px solid var(--border-soft);
  z-index: 2;
}
.brand { display: flex; align-items: baseline; gap: 8px; font-weight: 800; font-size: 1.12rem; color: var(--text); }
.brand:hover { text-decoration: none; }
.brand .logo { color: var(--accent); }
.brand span { font-weight: 500; font-size: .78rem; color: var(--text-dim); }

.nav { padding: 14px 12px; }
.nav-group { margin-bottom: 18px; }
.nav-group-title {
  display: flex; align-items: center; gap: 8px;
  font-size: .72rem; font-weight: 700; letter-spacing: .08em; text-transform: uppercase;
  color: var(--text-faint); padding: 6px 10px; margin-bottom: 4px;
}
.nav a {
  display: block;
  padding: 7px 12px 7px 26px;
  color: var(--text-dim);
  border-radius: 8px;
  font-size: .89rem;
  position: relative;
  transition: background .15s, color .15s;
}
.nav a:hover { background: var(--bg-card); color: var(--text); text-decoration: none; }
.nav a.active { background: rgba(20,184,166,.15); color: var(--accent-2); font-weight: 600; }
.nav a.active::before {
  content: ""; position: absolute; left: 10px; top: 50%; transform: translateY(-50%);
  width: 4px; height: 16px; background: var(--accent); border-radius: 4px;
}

.lvl { width: 9px; height: 9px; border-radius: 50%; display: inline-block; }
.lvl-basic { background: var(--basic); }
.lvl-inter { background: var(--inter); }
.lvl-adv   { background: var(--adv); }

/* ---------- Main ---------- */
.main { margin-left: var(--sidebar-w); flex: 1; min-width: 0; }
.content { max-width: 880px; margin: 0 auto; padding: 48px 40px 100px; }

/* breadcrumb / level badge */
.crumb { display: flex; align-items: center; gap: 10px; font-size: .82rem; color: var(--text-faint); margin-bottom: 14px; }
.badge {
  display: inline-flex; align-items: center; gap: 6px;
  padding: 3px 11px; border-radius: 999px; font-size: .74rem; font-weight: 700;
  letter-spacing: .03em; text-transform: uppercase;
}
.badge-basic { background: rgba(34,197,94,.14); color: #4ade80; border: 1px solid rgba(34,197,94,.3); }
.badge-inter { background: rgba(245,158,11,.14); color: #fbbf24; border: 1px solid rgba(245,158,11,.3); }
.badge-adv   { background: rgba(239,68,68,.14); color: #f87171; border: 1px solid rgba(239,68,68,.3); }

/* ---------- Typography ---------- */
h1 { font-size: 2.1rem; line-height: 1.2; margin: 6px 0 10px; font-weight: 800; letter-spacing: -.02em; }
h2 {
  font-size: 1.5rem; margin: 48px 0 14px; font-weight: 700; letter-spacing: -.01em;
  padding-bottom: 8px; border-bottom: 1px solid var(--border-soft);
}
h3 { font-size: 1.18rem; margin: 32px 0 10px; font-weight: 700; color: var(--accent-2); }
h4 { font-size: 1rem; margin: 22px 0 8px; font-weight: 700; color: var(--text); }
p { margin: 12px 0; }
.lead { font-size: 1.12rem; color: var(--text-dim); margin: 8px 0 26px; }

ul, ol { padding-left: 24px; margin: 12px 0; }
li { margin: 7px 0; }
li::marker { color: var(--accent); }

strong { color: #fff; font-weight: 700; }
hr { border: none; border-top: 1px solid var(--border); margin: 40px 0; }

/* inline code */
:not(pre) > code {
  font-family: var(--mono);
  background: var(--bg-card);
  border: 1px solid var(--border-soft);
  padding: 2px 6px;
  border-radius: 6px;
  font-size: .85em;
  color: #5eead4;
  white-space: nowrap;
}

/* ---------- Code blocks ---------- */
.code-block { margin: 18px 0; border-radius: var(--radius); overflow: hidden; border: 1px solid var(--border); background: var(--bg-code); }
.code-head {
  display: flex; align-items: center; justify-content: space-between;
  padding: 8px 14px; background: #081210; border-bottom: 1px solid var(--border);
  font-family: var(--mono); font-size: .78rem; color: var(--text-dim);
}
.code-head .fname { display: flex; align-items: center; gap: 8px; }
.code-head .dot { width: 8px; height: 8px; border-radius: 50%; background: #25403a; }
.code-head .lang { font-size: .68rem; text-transform: uppercase; letter-spacing: .05em; color: var(--text-faint); padding: 2px 7px; border: 1px solid var(--border); border-radius: 5px; }
.copy-btn {
  background: transparent; border: 1px solid var(--border); color: var(--text-dim);
  font-size: .72rem; padding: 3px 10px; border-radius: 6px; cursor: pointer; font-family: var(--sans);
  transition: all .15s;
}
.copy-btn:hover { background: var(--accent); color: #04201c; border-color: var(--accent); }
.copy-btn.copied { background: var(--basic); color: #06240f; border-color: var(--basic); }
pre { margin: 0; padding: 16px 18px; overflow-x: auto; font-size: .86rem; line-height: 1.6; }
pre code { font-family: var(--mono); background: none; border: none; padding: 0; white-space: pre; color: #cfe3df; }

/* ---------- Callouts ---------- */
.note { border-radius: var(--radius); padding: 14px 18px 14px 16px; margin: 20px 0; border-left: 4px solid; font-size: .94rem; background: var(--bg-card); }
.note p:first-child { margin-top: 0; } .note p:last-child { margin-bottom: 0; }
.note-title { font-weight: 700; display: block; margin-bottom: 4px; }
.note.tip { border-color: var(--basic); } .note.tip .note-title { color: #4ade80; }
.note.info { border-color: var(--accent); } .note.info .note-title { color: var(--accent-2); }
.note.warn { border-color: var(--inter); } .note.warn .note-title { color: #fbbf24; }
.note.danger { border-color: var(--adv); } .note.danger .note-title { color: #f87171; }

/* ---------- Tables ---------- */
.table-wrap { overflow-x: auto; margin: 18px 0; }
table { border-collapse: collapse; width: 100%; font-size: .89rem; }
th, td { text-align: left; padding: 10px 14px; border: 1px solid var(--border); vertical-align: top; }
th { background: var(--bg-card); font-weight: 700; color: var(--text); }
td { color: var(--text-dim); }
tr:nth-child(even) td { background: var(--bg-soft); }
td code, th code { white-space: nowrap; }

/* ---------- Prev / Next ---------- */
.pager { display: flex; gap: 16px; margin-top: 60px; padding-top: 28px; border-top: 1px solid var(--border); }
.pager a {
  flex: 1; padding: 16px 18px; border: 1px solid var(--border); border-radius: var(--radius);
  background: var(--bg-card); transition: border-color .15s, transform .15s;
}
.pager a:hover { border-color: var(--accent); text-decoration: none; transform: translateY(-2px); }
.pager .dir { font-size: .75rem; color: var(--text-faint); }
.pager .ttl { font-weight: 600; color: var(--text); margin-top: 2px; }
.pager .next { text-align: right; }

/* ---------- Misc ---------- */
.kbd { font-family: var(--mono); font-size: .8em; background: var(--bg-card); border: 1px solid var(--border); border-bottom-width: 2px; border-radius: 6px; padding: 1px 7px; }
.pill { display:inline-block; padding:1px 8px; border-radius:6px; font-size:.78rem; font-family:var(--mono); }
.pill-a { background: rgba(20,184,166,.16); color:#5eead4; }
.pill-b { background: rgba(245,158,11,.15); color:#fcd34d; }
/* ASCII / diagram block */
.diagram { background: var(--bg-code); border: 1px dashed var(--border); border-radius: var(--radius); padding: 14px 16px; margin: 18px 0; font-family: var(--mono); font-size: .82rem; color: var(--accent-2); overflow-x: auto; white-space: pre; line-height: 1.5; }

/* Hình minh họa (diagram từ repo gốc) */
.fig { margin: 24px 0; }
.fig img {
  display: block; width: 100%; height: auto;
  background: #fff; padding: 12px; border-radius: 10px;
  border: 1px solid var(--border);
}
.fig.fig-sm img { max-width: 460px; margin: 0 auto; }
.fig.fig-md img { max-width: 640px; margin: 0 auto; }
.fig figcaption {
  text-align: center; font-size: .82rem; color: var(--text-faint);
  margin-top: 8px; font-style: italic;
}
.fig figcaption b { color: var(--accent-2); font-style: normal; }

/* mobile toggle */
.menu-btn { display: none; position: fixed; top: 14px; left: 14px; z-index: 50;
  background: var(--bg-card); border: 1px solid var(--border); color: var(--text);
  width: 42px; height: 42px; border-radius: 10px; font-size: 1.2rem; cursor: pointer; }
.overlay { display: none; position: fixed; inset: 0; background: rgba(0,0,0,.55); z-index: 39; }

@media (max-width: 1024px) {
  .menu-btn { display: block; }
  .sidebar { transform: translateX(-100%); transition: transform .25s ease; }
  .sidebar.open { transform: translateX(0); }
  .overlay.show { display: block; }
  .main { margin-left: 0; }
  .content { padding: 64px 22px 80px; }
}