/* ══════════════════════════════════════════════════════
   Interview Prep — style.css  v3
   Documentation-grade dark theme · NeetCode-inspired
   ══════════════════════════════════════════════════════ */
@import url('https://fonts.googleapis.com/css2?family=Inter:wght@400;500;600;700;800&family=JetBrains+Mono:wght@400;500&display=swap');

/* ── Design Tokens ────────────────────────────────── */
:root {
  --bg-base:      #0e1117;
  --bg-surface:   #141920;
  --bg-card:      #1a2232;
  --bg-elevated:  #1e2a3a;
  --bg-overlay:   #243346;
  --bg-hover:     #1c2840;
  --bg-input:     #111720;
  --bg-code:      #0b1320;

  --border-faint:   #1a2535;
  --border:         #222f42;
  --border-default: #2c3f58;
  --border-strong:  #3d5878;

  --text-primary:   #e6f0fb;
  --text-secondary: #8aabcc;
  --text-muted:     #4a6484;
  --text-dim:       #243040;

  --blue:          #5aacff;
  --blue-dim:      rgba(90,172,255,.10);
  --blue-glow:     rgba(90,172,255,.20);
  --green:         #3ecb7a;
  --green-dim:     rgba(62,203,122,.09);
  --amber:         #f5a523;
  --amber-dim:     rgba(245,165,35,.09);
  --red:           #f05252;
  --red-dim:       rgba(240,82,82,.10);
  --purple:        #a78bfa;
  --purple-dim:    rgba(167,139,250,.10);
  --cyan:          #22d3ee;
  --cyan-dim:      rgba(34,211,238,.09);
  --teal:          #14b8a6;

  /* Legacy compat */
  --bg-secondary: #141920;
  --accent-blue:  #5aacff;
  --accent-green: #3ecb7a;
  --accent-orange:#f5a523;
  --accent-red:   #f05252;
  --accent-purple:#a78bfa;
  --accent-cyan:  #22d3ee;
  --accent-yellow:#f5a523;

  --sidebar-width: 268px;
  --r-sm: 4px;  --r: 6px;  --r-md: 8px;  --r-lg: 12px;  --r-xl: 16px;
  --shadow-sm:  0 1px 4px rgba(0,0,0,.45);
  --shadow:     0 4px 24px rgba(0,0,0,.55);
  --shadow-lg:  0 8px 48px rgba(0,0,0,.75);
}

*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }
html { font-size: 15px; scroll-behavior: smooth; }
body {
  font-family: 'Inter', -apple-system, BlinkMacSystemFont, 'Segoe UI', sans-serif;
  background: var(--bg-base);
  color: var(--text-primary);
  line-height: 1.65;
  display: flex;
  min-height: 100vh;
  -webkit-font-smoothing: antialiased;
  -moz-osx-font-smoothing: grayscale;
}

::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: var(--border-default); border-radius: 4px; }
::-webkit-scrollbar-thumb:hover { background: var(--border-strong); }

/* ═══ SIDEBAR ════════════════════════════════════════ */
.sidebar {
  width: var(--sidebar-width);
  background: var(--bg-surface);
  border-right: 1px solid var(--border);
  position: fixed;
  top: 0; left: 0; bottom: 0;
  overflow-y: auto;
  z-index: 200;
  display: flex;
  flex-direction: column;
}
.sidebar-logo {
  display: flex;
  align-items: center;
  gap: 11px;
  padding: 20px 18px 16px;
  border-bottom: 1px solid var(--border);
  flex-shrink: 0;
}
.logo-mark {
  display: flex;
  align-items: center;
  justify-content: center;
  width: 34px; height: 34px;
  background: linear-gradient(135deg, var(--blue), var(--purple));
  border-radius: var(--r-md);
  font-size: 11px; font-weight: 800;
  color: #fff; letter-spacing: .5px; flex-shrink: 0;
  box-shadow: 0 2px 10px rgba(90,172,255,.25);
}
.sidebar-logo h2 { font-size: 14px; font-weight: 700; color: var(--text-primary); letter-spacing: -.1px; }
.sidebar-logo p  { font-size: 11px; color: var(--text-muted); margin-top: 1px; }
.sidebar-nav { padding: 10px 0 8px; flex: 1; }
.nav-section-label {
  padding: 16px 18px 5px;
  font-size: 10px; font-weight: 700; letter-spacing: 1.4px;
  text-transform: uppercase; color: var(--text-muted);
}
.nav-link {
  display: flex;
  align-items: center;
  padding: 9px 18px;
  color: var(--text-secondary);
  text-decoration: none;
  font-size: 14px; font-weight: 500;
  border-left: 2px solid transparent;
  transition: all .12s;
  margin: 1px 0;
  line-height: 1.3;
}
.nav-link:hover { background: var(--bg-hover); color: var(--text-primary); border-left-color: var(--border-default); }
.nav-link.active { background: var(--blue-dim); color: var(--blue); border-left-color: var(--blue); font-weight: 600; }
.nav-link .icon { display: none; }
.nav-badge {
  margin-left: auto;
  background: var(--red); color: #fff;
  font-size: 9px; font-weight: 700;
  padding: 2px 6px; border-radius: 10px; letter-spacing: .3px;
}
.sidebar-footer {
  padding: 13px 18px;
  border-top: 1px solid var(--border);
  font-size: 12px; color: var(--text-muted);
  display: flex; align-items: center; gap: 8px; flex-shrink: 0;
}

/* ═══ TOPBAR ════════════════════════════════════════ */
.main { margin-left: var(--sidebar-width); flex: 1; min-height: 100vh; }
.topbar {
  position: sticky; top: 0;
  height: 54px;
  background: rgba(14,17,23,.95);
  backdrop-filter: blur(16px);
  -webkit-backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
  padding: 0 32px;
  z-index: 100;
  display: flex; align-items: center; gap: 14px;
}
.topbar h1 { font-size: 15px; font-weight: 700; flex: 1; color: var(--text-secondary); letter-spacing: -.1px; }
.topbar-search-btn {
  display: flex; align-items: center; gap: 8px;
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--r); padding: 6px 13px;
  color: var(--text-muted); font-size: 13px;
  cursor: pointer; transition: all .12s; font-family: inherit;
  white-space: nowrap;
}
.topbar-search-btn:hover { border-color: var(--blue); color: var(--text-secondary); }
.search-box {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--r); padding: 6px 13px;
  color: var(--text-primary); font-size: 14px; width: 240px;
  outline: none; transition: border-color .12s; font-family: inherit;
}
.search-box:focus { border-color: var(--blue); }
.search-box::placeholder { color: var(--text-muted); }

/* ═══ SPOTLIGHT SEARCH ══════════════════════════════ */
.spotlight-overlay {
  position: fixed; inset: 0;
  background: rgba(4,9,17,.80);
  backdrop-filter: blur(8px);
  -webkit-backdrop-filter: blur(8px);
  z-index: 9999;
  display: flex; align-items: flex-start; justify-content: center;
  padding-top: 80px;
  animation: sp-in .12s ease;
}
@keyframes sp-in { from { opacity:0 } to { opacity:1 } }
.spotlight-modal {
  background: var(--bg-elevated);
  border: 1px solid var(--border-default);
  border-radius: var(--r-xl);
  width: 620px; max-width: calc(100vw - 32px);
  max-height: calc(100vh - 110px);
  display: flex; flex-direction: column; overflow: hidden;
  box-shadow: var(--shadow-lg);
  animation: sp-modal .14s ease;
}
@keyframes sp-modal { from { opacity:0; transform:scale(.97) translateY(-6px) } to { opacity:1; transform:scale(1) translateY(0) } }
.spotlight-header {
  display: flex; align-items: center; gap: 12px;
  padding: 16px 18px;
  border-bottom: 1px solid var(--border);
}
.spotlight-header svg { width: 18px; height: 18px; color: var(--text-muted); flex-shrink: 0; }
.spotlight-input {
  flex: 1; background: transparent; border: none; outline: none;
  color: var(--text-primary); font-size: 17px; font-family: inherit; font-weight: 500;
}
.spotlight-input::placeholder { color: var(--text-muted); }
.spotlight-esc {
  background: var(--bg-overlay); border: 1px solid var(--border-default);
  border-radius: var(--r-sm); padding: 2px 8px;
  font-size: 11px; color: var(--text-muted); font-family: inherit; cursor: pointer;
}
.spotlight-results { overflow-y: auto; max-height: 400px; padding: 6px 0; }
.spotlight-group-label {
  padding: 8px 18px 4px;
  font-size: 10px; font-weight: 700; letter-spacing: 1px;
  text-transform: uppercase; color: var(--text-muted);
}
.spotlight-item {
  display: flex; align-items: center; gap: 12px;
  padding: 10px 18px; cursor: pointer; transition: background .08s;
  text-decoration: none;
}
.spotlight-item:hover, .spotlight-item.sp-active { background: var(--blue-dim); }
.spotlight-item-icon {
  width: 32px; height: 32px;
  border-radius: var(--r-sm);
  background: var(--bg-overlay);
  border: 1px solid var(--border-default);
  display: flex; align-items: center; justify-content: center;
  flex-shrink: 0; font-size: 11px; font-weight: 700;
  color: var(--blue); font-family: 'JetBrains Mono', monospace;
}
.spotlight-item-body { flex: 1; min-width: 0; }
.spotlight-item-title { font-size: 14px; font-weight: 600; color: var(--text-primary); }
.spotlight-item-sub { font-size: 12px; color: var(--text-muted); margin-top: 1px; white-space: nowrap; overflow: hidden; text-overflow: ellipsis; }
.spotlight-item mark { background: rgba(245,165,35,.25); color: var(--amber); border-radius: 2px; padding: 0 1px; }
.spotlight-empty { padding: 36px; text-align: center; color: var(--text-muted); font-size: 14px; }
.spotlight-footer {
  border-top: 1px solid var(--border);
  padding: 9px 18px;
  display: flex; align-items: center; gap: 16px;
  font-size: 12px; color: var(--text-muted);
}

/* ═══ CONTENT AREA ═══════════════════════════════════ */
.content-area { padding: 36px 40px; max-width: 960px; }
.section { display: none; }
.section.active { display: block; }
.section-header { margin-bottom: 32px; }
.section-header h1 { font-size: 28px; font-weight: 800; margin-bottom: 8px; letter-spacing: -.5px; color: var(--text-primary); }
.section-header p  { color: var(--text-secondary); font-size: 15px; line-height: 1.6; }

/* ═══ GRID ═══════════════════════════════════════════ */
.grid-2    { display: grid; grid-template-columns: 1fr 1fr; gap: 16px; }
.grid-3    { display: grid; grid-template-columns: 1fr 1fr 1fr; gap: 16px; }
.grid-auto { display: grid; grid-template-columns: repeat(auto-fill, minmax(280px,1fr)); gap: 16px; }

/* ═══ CARD ═══════════════════════════════════════════ */
.card { background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--r-md); overflow: hidden; transition: border-color .15s, box-shadow .15s; }
.card:hover { border-color: var(--border-default); box-shadow: var(--shadow-sm); }
.card-header { padding: 16px 18px 12px; border-bottom: 1px solid var(--border-faint); display: flex; align-items: flex-start; gap: 10px; }
.card-header h3 { font-size: 15px; font-weight: 700; flex: 1; }
.card-body { padding: 16px 18px; }
.card-body p { font-size: 14px; color: var(--text-secondary); margin-bottom: 9px; }

/* ═══ PROBLEM CARD ═══════════════════════════════════ */
.problem-card {
  background: var(--bg-card);
  border: 1px solid var(--border);
  border-radius: var(--r-lg);
  margin-bottom: 14px;
  overflow: hidden;
  transition: border-color .15s, box-shadow .15s;
}
.problem-card:hover { border-color: var(--border-default); box-shadow: 0 2px 16px rgba(0,0,0,.3); }
.problem-card-header {
  padding: 18px 20px;
  display: flex;
  align-items: center;
  gap: 12px;
  cursor: pointer;
  user-select: none;
  transition: background .1s;
}
.problem-card-header:hover { background: var(--bg-hover); }
.problem-card-header h3 {
  font-size: 16px;
  font-weight: 600;
  flex: 1;
  color: var(--text-primary);
  letter-spacing: -.1px;
  line-height: 1.35;
}
.problem-card-body {
  padding: 0 20px 20px;
  display: none;
  border-top: 1px solid var(--border-faint);
}
.problem-card-body.open { display: block; padding-top: 18px; }
.toggle-icon {
  color: var(--text-muted);
  font-size: 12px;
  transition: transform .2s;
  flex-shrink: 0;
  width: 20px; height: 20px;
  display: flex; align-items: center; justify-content: center;
  background: var(--bg-elevated);
  border-radius: var(--r-sm);
}
.problem-card-header.open .toggle-icon { transform: rotate(90deg); }

/* ═══ TABS ═══════════════════════════════════════════ */
.tabs {
  display: flex;
  gap: 0;
  margin-bottom: 16px;
  border-bottom: 1px solid var(--border);
  overflow-x: auto;
}
.tab-btn {
  padding: 8px 16px;
  border: none;
  border-bottom: 2px solid transparent;
  background: transparent;
  color: var(--text-muted);
  font-size: 13.5px; font-weight: 500;
  cursor: pointer; transition: all .12s; font-family: inherit;
  white-space: nowrap;
  margin-bottom: -1px;
}
.tab-btn.active {
  color: var(--blue);
  border-bottom-color: var(--blue);
  font-weight: 600;
}
.tab-btn:hover:not(.active) { color: var(--text-secondary); }
.tab-pane { display: none; }
.tab-pane.active { display: block; }

/* ═══ SOLUTION RANKING ═══════════════════════════════ */
.solution-rank { display: flex; flex-direction: column; gap: 8px; margin: 14px 0 18px; }
.rank-item {
  display: flex; align-items: flex-start; gap: 12px;
  padding: 12px 14px; border-radius: var(--r-md); border: 1px solid;
  font-size: 14px;
}
.rank-item.optimal    { background: var(--green-dim);  border-color: rgba(62,203,122,.25); }
.rank-item.good       { background: var(--blue-dim);   border-color: rgba(90,172,255,.20); }
.rank-item.acceptable { background: var(--amber-dim);  border-color: rgba(245,165,35,.22); }
.rank-item.poor       { background: var(--red-dim);    border-color: rgba(240,82,82,.22); }
.rank-label {
  font-size: 10px; font-weight: 700; letter-spacing: .5px; text-transform: uppercase;
  padding: 3px 8px; border-radius: 10px; white-space: nowrap; flex-shrink: 0; margin-top: 2px;
}
.optimal    .rank-label { background: var(--green);  color: #071510; }
.good       .rank-label { background: var(--blue);   color: #03101e; }
.acceptable .rank-label { background: var(--amber);  color: #1c0e00; }
.poor       .rank-label { background: var(--red);    color: #fff; }
.rank-content { flex: 1; }
.rank-content strong { color: var(--text-primary); display: block; margin-bottom: 3px; font-size: 14px; }
.rank-complexity { font-family: 'JetBrains Mono', monospace; font-size: 12px; color: var(--text-secondary); }

/* ═══ CODE ═══════════════════════════════════════════ */
pre {
  background: var(--bg-code) !important;
  border: 1px solid var(--border) !important;
  border-radius: var(--r-md) !important;
  padding: 18px 20px !important;
  overflow-x: auto;
  font-size: 13px !important;
  line-height: 1.7 !important;
  margin: 12px 0 !important;
  position: relative;
  font-family: 'JetBrains Mono', 'Fira Code', 'Cascadia Code', monospace !important;
}
code[class*="language-"] {
  font-size: 13px !important;
  font-family: 'JetBrains Mono', monospace !important;
  line-height: 1.7 !important;
}
.copy-btn {
  position: absolute; top: 10px; right: 10px;
  background: var(--bg-card); border: 1px solid var(--border-default);
  color: var(--text-muted); font-size: 11px; padding: 3px 9px;
  border-radius: var(--r-sm); cursor: pointer; transition: all .12s;
  z-index: 5; font-family: inherit; letter-spacing: .2px;
}
.copy-btn:hover { border-color: var(--blue); color: var(--blue); background: var(--blue-dim); }
:not(pre) > code {
  background: var(--bg-elevated); border: 1px solid var(--border-default);
  padding: 2px 6px; border-radius: var(--r-sm);
  font-size: 13px; font-family: 'JetBrains Mono', monospace; color: var(--cyan);
}
kbd {
  display: inline-flex; align-items: center;
  background: var(--bg-elevated); border: 1px solid var(--border-default);
  border-bottom: 2px solid var(--border-strong);
  border-radius: var(--r-sm); padding: 2px 7px;
  font-family: inherit; font-size: 12px; color: var(--text-secondary);
}

/* ═══ BADGES ═════════════════════════════════════════ */
.badge {
  display: inline-flex; align-items: center;
  font-size: 12px; font-weight: 600; padding: 3px 9px;
  border-radius: 20px; white-space: nowrap;
}
.badge-easy   { background: var(--green-dim);  color: var(--green);  border: 1px solid rgba(62,203,122,.3); }
.badge-medium { background: var(--amber-dim);  color: var(--amber);  border: 1px solid rgba(245,165,35,.3); }
.badge-hard   { background: var(--red-dim);    color: var(--red);    border: 1px solid rgba(240,82,82,.3); }
.badge-high   { background: var(--red-dim);    color: var(--red);    border: 1px solid rgba(240,82,82,.3); }
.badge-tag    { background: var(--blue-dim);   color: var(--blue);   border: 1px solid rgba(90,172,255,.25); }
.badge-purple { background: var(--purple-dim); color: var(--purple); border: 1px solid rgba(167,139,250,.25); }
.badge-green  { background: var(--green-dim);  color: var(--green);  border: 1px solid rgba(62,203,122,.3); }
.tag-row { display: flex; flex-wrap: wrap; gap: 6px; margin: 4px 0 2px; }

/* ═══ CALLOUT ════════════════════════════════════════ */
.callout {
  border-radius: var(--r-md);
  padding: 14px 16px;
  margin: 14px 0;
  font-size: 14px;
  border-left: 3px solid;
  line-height: 1.65;
}
.callout-blue   { background: var(--blue-dim);   border-color: var(--blue); }
.callout-green  { background: var(--green-dim);  border-color: var(--green); }
.callout-orange { background: var(--amber-dim);  border-color: var(--amber); }
.callout-red    { background: var(--red-dim);    border-color: var(--red); }
.callout-purple { background: var(--purple-dim); border-color: var(--purple); }
.callout-title  { font-weight: 700; margin-bottom: 5px; font-size: 13px; letter-spacing: .1px; }

/* ═══ TABLE ══════════════════════════════════════════ */
.table-wrap { overflow-x: auto; margin: 12px 0; border-radius: var(--r-md); border: 1px solid var(--border); }
table { width: 100%; border-collapse: collapse; font-size: 14px; margin: 12px 0; }
.table-wrap table { margin: 0; border-radius: var(--r-md); overflow: hidden; }
th {
  background: var(--bg-elevated);
  padding: 10px 14px;
  text-align: left;
  font-size: 12px; font-weight: 700;
  color: var(--text-muted); letter-spacing: .8px; text-transform: uppercase;
  border-bottom: 1px solid var(--border-default); white-space: nowrap;
}
td { padding: 11px 14px; border-bottom: 1px solid var(--border-faint); color: var(--text-secondary); vertical-align: top; line-height: 1.55; }
tr:last-child td { border-bottom: none; }
tr:hover td { background: var(--bg-hover); }
td code, th code {
  background: var(--bg-elevated); border: 1px solid var(--border-default);
  padding: 1px 6px; border-radius: var(--r-sm);
  font-size: 12px; font-family: 'JetBrains Mono', monospace; color: var(--cyan);
}
td strong { color: var(--text-primary); }

/* ═══ CONCEPT BOX ════════════════════════════════════ */
.concept-box {
  background: var(--bg-elevated);
  border: 1px solid var(--border);
  border-radius: var(--r-md);
  padding: 16px 18px;
  margin-bottom: 14px;
  font-size: 14px;
}
.concept-box h4 { color: var(--blue); margin-bottom: 10px; font-size: 11px; font-weight: 700; text-transform: uppercase; letter-spacing: .8px; }
.concept-box ul { padding-left: 20px; }
.concept-box li { margin-bottom: 6px; color: var(--text-secondary); line-height: 1.6; }
.concept-box p  { color: var(--text-secondary); line-height: 1.65; margin-bottom: 8px; }
.concept-box code {
  background: var(--bg-card); border: 1px solid var(--border-default);
  padding: 1px 6px; border-radius: var(--r-sm);
  font-size: 12.5px; font-family: 'JetBrains Mono', monospace; color: var(--cyan);
}

/* ═══ COMPLEXITY ══════════════════════════════════════ */
.complexity-box { display: flex; gap: 10px; margin-top: 12px; flex-wrap: wrap; }
.complexity-item {
  background: var(--bg-elevated); border: 1px solid var(--border-default);
  border-radius: var(--r-md); padding: 8px 14px;
  font-size: 13px; font-family: 'JetBrains Mono', monospace;
}
.complexity-item strong {
  color: var(--blue); display: block;
  font-size: 10px; text-transform: uppercase; letter-spacing: .6px; margin-bottom: 2px;
  font-family: 'Inter', sans-serif; font-weight: 700;
}

/* ═══ SUBSECTION ══════════════════════════════════════ */
.subsection { margin-bottom: 48px; }
.subsection-title {
  font-size: 20px;
  font-weight: 700;
  color: var(--text-primary);
  margin-bottom: 20px;
  padding-bottom: 12px;
  border-bottom: 1px solid var(--border);
  letter-spacing: -.3px;
  line-height: 1.3;
}

/* ═══ STAT CARD ══════════════════════════════════════ */
.stat-card { background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--r-md); padding: 20px 22px; text-align: center; }
.stat-card .stat-num   { font-size: 32px; font-weight: 800; letter-spacing: -1px; }
.stat-card .stat-label { font-size: 12px; color: var(--text-muted); margin-top: 5px; text-transform: uppercase; letter-spacing: .6px; }

/* ═══ TIMELINE ═══════════════════════════════════════ */
.timeline { position: relative; padding-left: 30px; }
.timeline::before { content: ''; position: absolute; left: 8px; top: 4px; bottom: 4px; width: 2px; background: var(--border-default); border-radius: 2px; }
.timeline-item { position: relative; margin-bottom: 18px; }
.timeline-item::before { content: ''; position: absolute; left: -26px; top: 5px; width: 11px; height: 11px; border-radius: 50%; background: var(--blue); border: 2px solid var(--bg-base); }
.timeline-item h4 { font-size: 14px; font-weight: 700; }
.timeline-item p  { font-size: 13.5px; color: var(--text-secondary); margin-top: 3px; }

/* ═══ ACCORDION ══════════════════════════════════════ */
.accordion { margin-bottom: 8px; }
.accordion-header { padding: 13px 18px; background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--r-md); cursor: pointer; display: flex; align-items: center; gap: 10px; font-size: 14px; font-weight: 600; transition: background .1s; user-select: none; }
.accordion-header:hover { background: var(--bg-hover); }
.accordion-header.open  { border-radius: var(--r-md) var(--r-md) 0 0; }
.accordion-body { background: var(--bg-card); border: 1px solid var(--border); border-top: none; border-radius: 0 0 var(--r-md) var(--r-md); padding: 0 18px; max-height: 0; overflow: hidden; transition: max-height .3s ease, padding .2s; }
.accordion-body.open { max-height: 4000px; padding: 16px 18px; }

/* ═══ MISC ═══════════════════════════════════════════ */
.highlight { background: rgba(245,165,35,.07); border-left: 3px solid var(--amber); padding: 11px 14px; border-radius: 0 var(--r-md) var(--r-md) 0; margin: 10px 0; font-size: 14px; color: var(--text-secondary); }
.checklist { list-style: none; padding: 0; }
.checklist li { display: flex; align-items: flex-start; gap: 9px; padding: 7px 0; font-size: 14px; color: var(--text-secondary); border-bottom: 1px solid var(--border-faint); }
.checklist li input[type=checkbox] { margin-top: 2px; accent-color: var(--green); cursor: pointer; }
.steps { counter-reset: steps; }
.step  { counter-increment: steps; display: flex; gap: 14px; margin-bottom: 14px; font-size: 14px; }
.step::before { content: counter(steps); min-width: 24px; height: 24px; background: var(--blue); color: #fff; border-radius: 50%; display: flex; align-items: center; justify-content: center; font-size: 12px; font-weight: 700; flex-shrink: 0; margin-top: 1px; }
.arch-box {
  background: var(--bg-code);
  border: 1px solid var(--border);
  border-radius: var(--r-md);
  padding: 18px 20px;
  font-family: 'JetBrains Mono', monospace;
  font-size: 12.5px;
  color: var(--text-secondary);
  line-height: 1.85;
  margin: 12px 0;
  white-space: pre;
  overflow-x: auto;
}
.section-jump { display: flex; flex-wrap: wrap; gap: 7px; margin-bottom: 28px; }
.jump-btn {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: 20px; padding: 6px 14px;
  font-size: 13px; font-weight: 500; color: var(--text-secondary);
  text-decoration: none; transition: all .12s;
}
.jump-btn:hover { border-color: var(--blue); color: var(--blue); background: var(--blue-dim); }
.warn-box { background: var(--red-dim); border: 1px solid rgba(240,82,82,.25); border-radius: var(--r-md); padding: 14px 16px; margin: 12px 0; font-size: 14px; color: var(--text-primary); line-height: 1.65; }
.warn-box strong { color: var(--red); }
.ok-box  { background: var(--green-dim); border: 1px solid rgba(62,203,122,.25); border-radius: var(--r-md); padding: 14px 16px; margin: 12px 0; font-size: 14px; line-height: 1.65; }
.ok-box strong { color: var(--green); }
.state-diagram { background: var(--bg-code); border: 1px solid rgba(34,211,238,.18); border-radius: var(--r-md); padding: 16px 18px; font-family: 'JetBrains Mono', monospace; font-size: 12.5px; color: var(--cyan); line-height: 1.9; white-space: pre; overflow-x: auto; margin: 12px 0; }
.aws-badge { display: inline-block; background: rgba(255,153,0,.12); color: #ff9900; border: 1px solid rgba(255,153,0,.25); border-radius: var(--r-sm); padding: 2px 8px; font-size: 12px; font-weight: 700; }
.search-match { background: rgba(245,165,35,.25); border-radius: 2px; }

/* ═══ HERO (index) ═══════════════════════════════════ */
.hero {
  background: linear-gradient(135deg, rgba(90,172,255,.08), rgba(167,139,250,.06));
  border: 1px solid var(--border);
  border-radius: var(--r-xl);
  padding: 32px 36px;
  margin-bottom: 32px;
}
.hero h1 { font-size: 28px; font-weight: 800; margin-bottom: 8px; letter-spacing: -.5px; }
.hero p { color: var(--text-secondary); font-size: 15px; line-height: 1.6; }
.countdown { display: flex; gap: 24px; margin-top: 18px; }
.count-item { text-align: center; }
.count-num { font-size: 36px; font-weight: 800; color: var(--blue); line-height: 1; letter-spacing: -1px; }
.count-label { font-size: 11px; color: var(--text-muted); text-transform: uppercase; letter-spacing: 1px; margin-top: 3px; }
.topic-nav { display: grid; grid-template-columns: repeat(auto-fill, minmax(210px,1fr)); gap: 12px; margin-bottom: 32px; }
.topic-card {
  background: var(--bg-card); border: 1px solid var(--border);
  border-radius: var(--r-lg); padding: 18px 16px;
  text-decoration: none; color: var(--text-primary);
  transition: all .15s; display: flex; flex-direction: column; gap: 7px;
}
.topic-card:hover { border-color: var(--blue); box-shadow: 0 4px 20px rgba(90,172,255,.14); transform: translateY(-2px); }
.topic-card .t-icon { font-size: 0; }
.topic-card h3 { font-size: 14px; font-weight: 700; }
.topic-card p { font-size: 12px; color: var(--text-muted); line-height: 1.5; }
.topic-card .t-count { font-size: 12px; color: var(--blue); font-weight: 600; margin-top: auto; }
.interview-flow { background: var(--bg-card); border: 1px solid var(--border); border-radius: var(--r-lg); padding: 22px; margin-bottom: 26px; }
.interview-flow h3 { font-size: 15px; font-weight: 700; margin-bottom: 16px; }
.flow-row { display: grid; grid-template-columns: 1fr 1fr 1fr; gap: 14px; }
.flow-item { text-align: center; padding: 16px; background: var(--bg-elevated); border-radius: var(--r-md); border: 1px solid var(--border); }
.flow-item .f-time { font-size: 24px; font-weight: 800; color: var(--amber); }
.flow-item h4 { font-size: 14px; font-weight: 700; margin: 6px 0 4px; }
.flow-item p { font-size: 12px; color: var(--text-muted); }
.quick-ref { display: grid; grid-template-columns: 1fr 1fr; gap: 18px; }

/* ═══ RESPONSIVE ══════════════════════════════════════ */
@media (max-width: 1100px) {
  .grid-3 { grid-template-columns: 1fr 1fr; }
  .content-area { padding: 28px 28px; }
}
@media (max-width: 768px) {
  .sidebar { display: none; }
  .main { margin-left: 0; }
  .grid-2, .grid-3 { grid-template-columns: 1fr; }
  .content-area { padding: 20px 18px; }
  .flow-row { grid-template-columns: 1fr; }
  .quick-ref { grid-template-columns: 1fr; }
}
@media (max-width: 560px) {
  .content-area { padding: 16px 14px; }
  .problem-card-header { padding: 14px 16px; }
  .problem-card-header h3 { font-size: 15px; }
  .problem-card-body { padding: 0 16px 16px; }
}