/* ============================================================
   System Design & Highload — Interview Workbook
   Shared design system
   ============================================================ */

:root {
  /* Palette */
  --bg: #0f1220;
  --bg-2: #151a2d;
  --surface: #ffffff;
  --surface-2: #f7f8fc;
  --surface-3: #eef1f8;
  --ink: #1b2033;
  --ink-soft: #4a5169;
  --ink-faint: #79809a;
  --line: #e2e6f0;
  --line-strong: #cdd3e4;

  /* Accents */
  --brand: #5b6cff;
  --brand-2: #7c4dff;
  --teal: #12b5a5;
  --amber: #f5a623;
  --rose: #f2545b;
  --green: #23b26d;
  --sky: #2aa8f2;

  /* Callout tints */
  --tip-bg: #eafaf3;   --tip-line: #23b26d;
  --warn-bg: #fdf1e3;  --warn-line: #f5a623;
  --key-bg: #eef0ff;   --key-line: #5b6cff;
  --danger-bg: #fdecee;--danger-line: #f2545b;
  --quiz-bg: #f2ecfe;  --quiz-line: #7c4dff;

  --radius: 14px;
  --radius-sm: 9px;
  --shadow: 0 1px 2px rgba(20,25,50,.06), 0 8px 24px rgba(20,25,50,.06);
  --shadow-lg: 0 12px 40px rgba(20,25,50,.14);
  --mono: "SFMono-Regular", ui-monospace, "Cascadia Code", "JetBrains Mono", Consolas, monospace;
  --sans: "Inter", system-ui, -apple-system, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  --sidebar-w: 288px;
  --maxw: 980px;
}

* { box-sizing: border-box; }

html { scroll-behavior: smooth; }

body {
  margin: 0;
  font-family: var(--sans);
  color: var(--ink);
  background:
    radial-gradient(1200px 600px at 100% -10%, #eef1ff 0%, rgba(238,241,255,0) 60%),
    radial-gradient(1000px 500px at -10% 110%, #e9fbf7 0%, rgba(233,251,247,0) 55%),
    var(--surface-2);
  line-height: 1.6;
  -webkit-font-smoothing: antialiased;
  text-rendering: optimizeLegibility;
}

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

.sidebar {
  width: var(--sidebar-w);
  flex: 0 0 var(--sidebar-w);
  position: sticky;
  top: 0;
  align-self: flex-start;
  height: 100vh;
  overflow-y: auto;
  background: linear-gradient(180deg, #12162a 0%, #171d38 100%);
  color: #c9cfe6;
  padding: 26px 20px 40px;
  border-right: 1px solid rgba(255,255,255,.06);
}

.sidebar .brand {
  display: flex; align-items: center; gap: 12px;
  margin-bottom: 26px; padding: 4px;
}
.sidebar .brand .logo {
  width: 40px; height: 40px; border-radius: 11px;
  background: linear-gradient(135deg, var(--brand), var(--brand-2));
  display: grid; place-items: center; color: #fff; font-weight: 800;
  box-shadow: 0 6px 18px rgba(91,108,255,.5);
  flex: 0 0 auto;
}
.sidebar .brand b { color: #fff; font-size: 15px; display:block; letter-spacing:.2px;}
.sidebar .brand span { font-size: 12px; color: #8b93b6; }

.nav-group { margin: 18px 0 8px; font-size: 11px; text-transform: uppercase; letter-spacing: .12em; color: #6f77a0; padding-left: 10px; }

.sidebar a.nav {
  display: flex; align-items: center; gap: 11px;
  padding: 9px 12px; border-radius: 10px;
  color: #c3c9e4; text-decoration: none; font-size: 14px; font-weight: 500;
  margin-bottom: 2px; transition: background .15s, color .15s, transform .1s;
}
.sidebar a.nav:hover { background: rgba(255,255,255,.06); color: #fff; }
.sidebar a.nav.active { background: linear-gradient(90deg, rgba(91,108,255,.28), rgba(124,77,255,.12)); color: #fff; }
.sidebar a.nav .ic { width: 22px; text-align: center; opacity: .9; }
.sidebar a.nav .num {
  width: 22px; height: 22px; border-radius: 7px; display:grid; place-items:center;
  background: rgba(255,255,255,.08); font-size: 12px; font-weight: 700; color:#aeb6dc; flex:0 0 auto;
}
.sidebar a.nav.active .num { background: rgba(255,255,255,.18); color:#fff; }

.sidebar .foot { margin-top: 30px; font-size: 11.5px; color: #6b7397; padding: 0 10px; line-height:1.5;}

/* ---------------- Main ---------------- */
.main { flex: 1; min-width: 0; }
.content { max-width: var(--maxw); margin: 0 auto; padding: 46px 40px 120px; }

.page-hero {
  background: linear-gradient(135deg, #1a2040 0%, #2a2160 55%, #3a2a72 100%);
  color: #fff; border-radius: 20px; padding: 34px 36px; margin-bottom: 34px;
  position: relative; overflow: hidden; box-shadow: var(--shadow-lg);
}
.page-hero::after {
  content:""; position:absolute; right:-60px; top:-60px; width: 260px; height: 260px;
  background: radial-gradient(circle, rgba(124,77,255,.55), transparent 70%);
  filter: blur(6px);
}
.page-hero .kicker { font-size: 12px; letter-spacing: .16em; text-transform: uppercase; color: #b9b0ff; font-weight: 700; }
.page-hero h1 { margin: 8px 0 10px; font-size: 32px; line-height: 1.15; letter-spacing: -.5px; }
.page-hero p { margin: 0; color: #d7d9f0; max-width: 680px; font-size: 15.5px; }
.page-hero .chips { margin-top: 18px; display: flex; flex-wrap: wrap; gap: 8px; position: relative; z-index:1;}
.page-hero .chips span {
  background: rgba(255,255,255,.12); border: 1px solid rgba(255,255,255,.16);
  padding: 5px 11px; border-radius: 999px; font-size: 12.5px; font-weight: 500;
}

/* ---------------- Typography ---------------- */
h2.sec {
  font-size: 23px; letter-spacing: -.3px; margin: 46px 0 14px; padding-top: 8px;
  display: flex; align-items: center; gap: 12px;
}
h2.sec .dot { width: 12px; height: 12px; border-radius: 4px; background: linear-gradient(135deg,var(--brand),var(--brand-2)); flex:0 0 auto;}
h3.sub { font-size: 17.5px; margin: 26px 0 8px; color: var(--ink); }
h4.mini { font-size: 14px; text-transform: uppercase; letter-spacing: .08em; color: var(--ink-faint); margin: 20px 0 8px; }
p { margin: 10px 0; color: var(--ink-soft); }
.lead { font-size: 16.5px; color: var(--ink-soft); }
a { color: var(--brand); }
strong { color: var(--ink); }
ul, ol { color: var(--ink-soft); padding-left: 22px; }
li { margin: 5px 0; }
hr.soft { border: 0; border-top: 1px solid var(--line); margin: 34px 0; }

/* ---------------- Cards ---------------- */
.card {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 22px 24px; box-shadow: var(--shadow); margin: 16px 0;
}
.card.pad-lg { padding: 26px 28px; }
.grid { display: grid; gap: 16px; }
.grid.c2 { grid-template-columns: 1fr 1fr; }
.grid.c3 { grid-template-columns: 1fr 1fr 1fr; }
@media (max-width: 820px){ .grid.c2, .grid.c3 { grid-template-columns: 1fr; } }

.feature {
  background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 18px 20px; box-shadow: var(--shadow);
}
.feature .ficon {
  width: 40px; height: 40px; border-radius: 11px; display: grid; place-items: center;
  font-size: 20px; margin-bottom: 12px; color: #fff;
}
.feature h4 { margin: 0 0 6px; font-size: 15.5px; color: var(--ink); }
.feature p { margin: 0; font-size: 14px; }
.bg-brand { background: linear-gradient(135deg,var(--brand),var(--brand-2)); }
.bg-teal  { background: linear-gradient(135deg,var(--teal),#0c9a8b); }
.bg-amber { background: linear-gradient(135deg,var(--amber),#f2790f); }
.bg-rose  { background: linear-gradient(135deg,var(--rose),#d6336c); }
.bg-sky   { background: linear-gradient(135deg,var(--sky),#4361ee); }
.bg-green { background: linear-gradient(135deg,var(--green),#0ca678); }

/* ---------------- Callouts ---------------- */
.callout {
  border-radius: var(--radius-sm); padding: 14px 16px 14px 46px; margin: 16px 0;
  position: relative; font-size: 14.5px; border: 1px solid var(--line);
}
.callout::before {
  position: absolute; left: 14px; top: 13px; font-size: 18px; line-height: 1;
}
.callout .t { font-weight: 700; display: block; margin-bottom: 2px; color: var(--ink); }
.callout p { margin: 4px 0; }
.callout.tip   { background: var(--tip-bg);   border-left: 4px solid var(--tip-line); }
.callout.tip::before   { content: "✅"; }
.callout.warn  { background: var(--warn-bg);  border-left: 4px solid var(--warn-line); }
.callout.warn::before  { content: "⚠️"; }
.callout.key   { background: var(--key-bg);   border-left: 4px solid var(--key-line); }
.callout.key::before   { content: "🔑"; }
.callout.danger{ background: var(--danger-bg);border-left: 4px solid var(--danger-line); }
.callout.danger::before{ content: "🚨"; }
.callout.quiz  { background: var(--quiz-bg);  border-left: 4px solid var(--quiz-line); }
.callout.quiz::before  { content: "🎤"; }

/* interview soundbite */
.soundbite {
  border-left: 4px solid var(--brand-2); background: linear-gradient(90deg,#f4f0ff, #fbfaff);
  padding: 14px 18px; border-radius: 0 var(--radius-sm) var(--radius-sm) 0; margin: 14px 0;
  font-size: 15px; color: var(--ink); font-style: italic;
}
.soundbite b { font-style: normal; }

/* ---------------- Code ---------------- */
pre {
  background: #10142a; color: #e7ebff; border-radius: 12px; padding: 16px 18px;
  overflow-x: auto; font-family: var(--mono); font-size: 13px; line-height: 1.6;
  border: 1px solid #232a4d; margin: 14px 0;
}
pre .c { color: #7f88b5; }      /* comment */
pre .k { color: #ff9ecb; }      /* keyword */
pre .s { color: #b8f5c8; }      /* string */
pre .n { color: #ffd58a; }      /* number/const */
pre .m { color: #8fd0ff; }      /* method/verb */
pre .p { color: #c9cffa; }      /* punctuation dim */
code {
  font-family: var(--mono); font-size: .88em; background: var(--surface-3);
  padding: 2px 6px; border-radius: 6px; color: #3a3f70; border: 1px solid var(--line);
}
pre code { background: none; border: 0; padding: 0; color: inherit; font-size: 13px; }

.http { display: inline-block; font-family: var(--mono); font-weight: 700; font-size: 11.5px;
  padding: 2px 8px; border-radius: 6px; color: #fff; letter-spacing: .04em; }
.http.get { background: #23b26d; } .http.post { background: #2aa8f2; }
.http.put { background: #f5a623; } .http.del { background: #f2545b; }
.http.patch{ background: #7c4dff; }

/* ---------------- Tables ---------------- */
table { width: 100%; border-collapse: collapse; margin: 16px 0; font-size: 14px; background: var(--surface);
  border: 1px solid var(--line); border-radius: var(--radius); overflow: hidden; box-shadow: var(--shadow); }
thead th { background: var(--surface-3); text-align: left; padding: 11px 14px; font-size: 12.5px;
  text-transform: uppercase; letter-spacing: .05em; color: var(--ink-faint); font-weight: 700; }
td { padding: 11px 14px; border-top: 1px solid var(--line); color: var(--ink-soft); vertical-align: top; }
tbody tr:hover { background: var(--surface-2); }
td strong, td b { color: var(--ink); }

.badge { display:inline-block; padding: 2px 9px; border-radius: 999px; font-size: 12px; font-weight: 600; }
.badge.g { background: var(--tip-bg); color: #157347; }
.badge.a { background: var(--warn-bg); color: #a5610a; }
.badge.r { background: var(--danger-bg); color: #b02a37; }
.badge.b { background: var(--key-bg); color: #3b48c4; }

/* ---------------- Diagrams / SVG ---------------- */
.figure { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius);
  padding: 20px; box-shadow: var(--shadow); margin: 18px 0; }
.figure svg { display: block; width: 100%; height: auto; }
.figure figcaption, .figcap { text-align: center; font-size: 13px; color: var(--ink-faint); margin-top: 10px; }
.svg-label { font: 600 13px var(--sans); fill: var(--ink); }
.svg-sub { font: 500 11px var(--sans); fill: var(--ink-faint); }
.svg-mono { font: 600 12px var(--mono); }

/* two-column compare */
.compare { display: grid; grid-template-columns: 1fr 1fr; gap: 14px; margin: 16px 0; }
@media (max-width: 820px){ .compare { grid-template-columns: 1fr; } }
.compare .col { border-radius: var(--radius); padding: 16px 18px; border: 1px solid var(--line); }
.compare .col.good { background: var(--tip-bg); border-color: var(--tip-line); }
.compare .col.bad  { background: var(--danger-bg); border-color: var(--danger-line); }
.compare .col h4 { margin: 0 0 8px; display: flex; align-items: center; gap: 8px; }

/* step list */
.steps { counter-reset: step; list-style: none; padding: 0; margin: 16px 0; }
.steps > li { position: relative; padding: 4px 0 16px 46px; margin: 0; }
.steps > li::before {
  counter-increment: step; content: counter(step);
  position: absolute; left: 0; top: 0; width: 30px; height: 30px; border-radius: 50%;
  background: linear-gradient(135deg,var(--brand),var(--brand-2)); color: #fff;
  display: grid; place-items: center; font-weight: 700; font-size: 14px;
  box-shadow: 0 4px 10px rgba(91,108,255,.35);
}
.steps > li:not(:last-child)::after {
  content: ""; position: absolute; left: 14.5px; top: 32px; bottom: 2px; width: 2px; background: var(--line-strong);
}
.steps > li b { color: var(--ink); }

/* pill tags */
.tags { display: flex; flex-wrap: wrap; gap: 7px; margin: 10px 0; }
.tags .tag { background: var(--surface-3); border: 1px solid var(--line); color: var(--ink-soft);
  padding: 4px 11px; border-radius: 999px; font-size: 12.5px; font-weight: 500; }

/* KV stat row */
.stats { display: grid; grid-template-columns: repeat(auto-fit,minmax(140px,1fr)); gap: 12px; margin: 16px 0; }
.stat { background: var(--surface); border: 1px solid var(--line); border-radius: var(--radius); padding: 14px 16px; box-shadow: var(--shadow); }
.stat .v { font-size: 24px; font-weight: 800; color: var(--ink); letter-spacing: -.5px; }
.stat .l { font-size: 12.5px; color: var(--ink-faint); }

/* Table of contents on landing */
.toc-grid { display: grid; grid-template-columns: 1fr 1fr; gap: 18px; margin-top: 20px; }
@media (max-width: 820px){ .toc-grid { grid-template-columns: 1fr; } }
.toc-card {
  display: block; text-decoration: none; color: inherit; position: relative;
  background: var(--surface); border: 1px solid var(--line); border-radius: 16px;
  padding: 22px 24px; box-shadow: var(--shadow); transition: transform .15s, box-shadow .15s, border-color .15s;
  overflow: hidden;
}
.toc-card:hover { transform: translateY(-3px); box-shadow: var(--shadow-lg); border-color: var(--line-strong); }
.toc-card .n { position: absolute; right: 18px; top: 12px; font-size: 54px; font-weight: 800; color: var(--surface-3); line-height: 1; }
.toc-card h3 { margin: 0 0 6px; font-size: 18px; }
.toc-card p { margin: 0; font-size: 13.5px; }
.toc-card .tags { margin-top: 12px; }

/* Cheat card */
.cheat { background: linear-gradient(135deg,#101430,#1c2246); color:#dfe3f7; border-radius:16px; padding:22px 24px; margin:18px 0; box-shadow: var(--shadow-lg); }
.cheat h4 { color:#fff; margin:0 0 12px; font-size:15px; letter-spacing:.02em; }
.cheat ul { color:#c3c9e6; margin:0; padding-left: 20px;}
.cheat li { margin:6px 0; }
.cheat code { background: rgba(255,255,255,.08); color:#b8f5c8; border-color: rgba(255,255,255,.12); }

/* footer nav */
.pager { display:flex; justify-content:space-between; gap:14px; margin-top: 50px; }
.pager a { flex:1; text-decoration:none; border:1px solid var(--line); border-radius: var(--radius); padding:16px 18px;
  background: var(--surface); box-shadow: var(--shadow); transition: border-color .15s, transform .12s; }
.pager a:hover { border-color: var(--brand); transform: translateY(-2px); }
.pager a.next { text-align:right; }
.pager a .lbl { font-size:12px; color: var(--ink-faint); text-transform:uppercase; letter-spacing:.08em; }
.pager a .ttl { font-size:15px; font-weight:700; color: var(--ink); }

.mobile-top { display:none; }

@media (max-width: 900px){
  .sidebar { position: fixed; z-index: 50; transform: translateX(-100%); transition: transform .25s; box-shadow: var(--shadow-lg); }
  .sidebar.open { transform: translateX(0); }
  .content { padding: 22px 18px 90px; }
  .mobile-top { display:flex; align-items:center; gap:12px; position: sticky; top:0; z-index:40;
    background: rgba(255,255,255,.9); backdrop-filter: blur(8px); padding: 12px 16px; border-bottom: 1px solid var(--line); }
  .mobile-top button { border:1px solid var(--line); background:#fff; border-radius:10px; width:40px; height:40px; font-size:18px; }
  .page-hero h1 { font-size: 25px; }
}

@media print {
  .sidebar, .pager, .mobile-top { display: none !important; }
  body { background: #fff; }
  .card, .figure, table, .feature { break-inside: avoid; box-shadow: none; }
  .page-hero { background: #1a2040 !important; -webkit-print-color-adjust: exact; print-color-adjust: exact; }
  * { -webkit-print-color-adjust: exact; print-color-adjust: exact; }
}