/* ═══════════════════════════════════════════════
   shared.css — DSA Mastery Hub · Shared Styles
   Used by all 16 topic pages
═══════════════════════════════════════════════ */

/* ── Reset & Tokens ── */
*, *::before, *::after { box-sizing: border-box; margin: 0; padding: 0; }

:root {
  --bg:       #070b14;
  --surface:  #0d1220;
  --surface2: #131927;
  --border:   rgba(255,255,255,0.07);
  --text:     #e8eaf6;
  --text2:    #9ba3c0;
  --text3:    #5c6482;
  --accent:   #6c63ff;
  --accent2:  #9d96ff;
  --blue:     #60a5fa;
  --good:     #34d399;
  --ok:       #fbbf24;
  --bad:      #f87171;
  --purple:   #c084fc;
  --code-bg:  #0a0e1a;
  --radius:   14px;
  --radius-sm: 8px;
}

html { scroll-behavior: smooth; }

body {
  background: var(--bg);
  color: var(--text);
  font-family: 'Inter', system-ui, -apple-system, sans-serif;
  font-size: 15px;
  line-height: 1.7;
  min-height: 100vh;
}

/* ── Top Nav ── */
.top-nav {
  position: sticky;
  top: 0;
  z-index: 100;
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding: 0 20px;
  height: 54px;
  background: rgba(7,11,20,0.9);
  backdrop-filter: blur(16px);
  border-bottom: 1px solid var(--border);
}

.nav-back {
  display: flex;
  align-items: center;
  gap: 8px;
  color: var(--text2);
  text-decoration: none;
  font-size: 13px;
  font-weight: 600;
  padding: 6px 12px;
  border-radius: 8px;
  border: 1px solid var(--border);
  transition: all 0.2s;
}
.nav-back:hover { color: var(--text); background: var(--surface2); border-color: var(--accent); }

.nav-title {
  font-size: 14px;
  font-weight: 700;
  color: var(--text);
}

.nav-num {
  font-size: 12px;
  font-weight: 600;
  color: var(--text3);
  font-family: 'Fira Code', monospace;
  background: var(--surface2);
  padding: 4px 10px;
  border-radius: 20px;
  border: 1px solid var(--border);
}

/* ── Hero ── */
.page-hero {
  background: linear-gradient(180deg, rgba(108,99,255,0.06) 0%, transparent 100%);
  border-bottom: 1px solid var(--border);
  padding: 48px 20px 36px;
}

.page-hero-inner {
  max-width: 760px;
  margin: 0 auto;
}

.topic-badge {
  display: inline-flex;
  align-items: center;
  gap: 6px;
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.5px;
  padding: 5px 12px;
  border-radius: 20px;
  margin-bottom: 14px;
  text-transform: uppercase;
}

.page-hero h1 {
  font-size: clamp(28px, 5vw, 42px);
  font-weight: 800;
  letter-spacing: -0.5px;
  color: var(--text);
  margin-bottom: 10px;
  line-height: 1.2;
}

.page-hero p {
  font-size: 16px;
  color: var(--text2);
  max-width: 620px;
}

.complexity-pills {
  display: flex;
  gap: 10px;
  margin-top: 16px;
  flex-wrap: wrap;
}
.pill {
  font-size: 12px;
  color: var(--text3);
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: 20px;
  padding: 4px 12px;
}
.pill span { color: var(--accent2); font-weight: 600; }

/* ── Main Layout ── */
.page-main {
  max-width: 900px;
  margin: 0 auto;
  padding: 28px 16px 80px;
}

/* ── Tabs ── */
.section-tabs {
  display: flex;
  gap: 4px;
  margin-bottom: 24px;
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 5px;
  overflow-x: auto;
  scrollbar-width: none;
}
.section-tabs::-webkit-scrollbar { display: none; }

.tab-btn {
  display: flex;
  align-items: center;
  gap: 7px;
  padding: 9px 16px;
  border: none;
  border-radius: 10px;
  background: transparent;
  color: var(--text2);
  font-size: 13px;
  font-weight: 600;
  font-family: 'Inter', sans-serif;
  cursor: pointer;
  white-space: nowrap;
  transition: all 0.2s;
  flex-shrink: 0;
}
.tab-btn:hover { color: var(--text); background: var(--surface2); }
.tab-btn.active { background: var(--accent); color: #fff; box-shadow: 0 4px 14px rgba(108,99,255,0.35); }

.tab-content { display: none; }
.tab-content.active { display: block; animation: fadeIn 0.25s ease; }

@keyframes fadeIn { from { opacity: 0; transform: translateY(6px); } to { opacity: 1; transform: translateY(0); } }

/* ── Card ── */
.card {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  padding: 24px;
  margin-bottom: 20px;
}

.card-header {
  display: flex;
  align-items: center;
  gap: 14px;
  margin-bottom: 18px;
}
.card-icon {
  width: 44px; height: 44px;
  border-radius: 12px;
  display: flex; align-items: center; justify-content: center;
  font-size: 18px;
  flex-shrink: 0;
}
.card-header h3 {
  font-size: 18px;
  font-weight: 700;
}

.grid-2 {
  display: grid;
  grid-template-columns: 1fr 1fr;
  gap: 20px;
}
@media (max-width: 600px) { .grid-2 { grid-template-columns: 1fr; } }

/* ── Viz Container ── */
.viz-container {
  background: var(--surface);
  border: 1px solid var(--border);
  border-radius: var(--radius);
  overflow: hidden;
  margin-bottom: 20px;
}

.viz-header {
  background: var(--surface2);
  border-bottom: 1px solid var(--border);
  padding: 12px 18px;
}
.viz-title {
  font-size: 13px;
  font-weight: 700;
  color: var(--text);
  display: flex;
  align-items: center;
  gap: 8px;
  letter-spacing: 0.2px;
}
.viz-title i { color: var(--accent2); }

.viz-body { padding: 20px; }

.viz-controls {
  display: flex;
  gap: 8px;
  flex-wrap: wrap;
  margin-top: 16px;
}

.viz-info {
  margin-top: 16px;
  padding: 12px 16px;
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  font-size: 13px;
  color: var(--text2);
  min-height: 44px;
  line-height: 1.6;
}

/* ── Array Visualization ── */
.array-viz {
  display: flex;
  gap: 4px;
  flex-wrap: wrap;
  align-items: flex-end;
}

.arr-cell {
  min-width: 46px;
  height: 52px;
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: 10px;
  background: rgba(255,255,255,0.04);
  border: 2px solid rgba(255,255,255,0.1);
  font-family: 'Fira Code', monospace;
  font-size: 15px;
  font-weight: 700;
  color: var(--text2);
  transition: all 0.3s cubic-bezier(0.34,1.56,0.64,1);
  position: relative;
}

.arr-cell-label {
  position: absolute;
  bottom: -18px;
  left: 50%;
  transform: translateX(-50%);
  font-size: 10px;
  font-family: 'Fira Code', monospace;
  white-space: nowrap;
}

/* Cell States */
.arr-cell.highlight { background: rgba(251,191,36,0.2); border-color: #fbbf24; color: #fbbf24; transform: scale(1.1) translateY(-4px); box-shadow: 0 8px 24px rgba(251,191,36,0.3); }
.arr-cell.found     { background: rgba(52,211,153,0.2); border-color: #34d399; color: #34d399; transform: scale(1.12) translateY(-6px); box-shadow: 0 8px 24px rgba(52,211,153,0.35); }
.arr-cell.left      { background: rgba(96,165,250,0.15); border-color: #60a5fa; color: #60a5fa; }
.arr-cell.right     { background: rgba(248,113,113,0.15); border-color: #f87171; color: #f87171; }
.arr-cell.mid       { background: rgba(192,132,252,0.2); border-color: #c084fc; color: #c084fc; transform: scale(1.08) translateY(-3px); box-shadow: 0 6px 18px rgba(192,132,252,0.3); }
.arr-cell.window    { background: rgba(108,99,255,0.15); border-color: rgba(108,99,255,0.5); color: var(--accent2); }

/* ── Code Blocks ── */
pre {
  background: var(--code-bg);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  padding: 18px 20px;
  font-family: 'Fira Code', monospace;
  font-size: 13px;
  line-height: 1.75;
  overflow-x: auto;
  color: #c5d0f0;
}

pre .kw  { color: #c084fc; font-weight: 600; }
pre .fn  { color: #67e8f9; }
pre .cm  { color: #4a5580; font-style: italic; }
pre .st  { color: #86efac; }
pre .nm  { color: #fb923c; }
pre .op  { color: #94a3b8; }

/* ── Tables ── */
table {
  width: 100%;
  border-collapse: collapse;
  font-size: 13px;
  margin: 12px 0;
}
th {
  padding: 10px 12px;
  text-align: left;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.5px;
  text-transform: uppercase;
  color: var(--text3);
  border-bottom: 1px solid var(--border);
}
td {
  padding: 10px 12px;
  border-bottom: 1px solid rgba(255,255,255,0.04);
  color: var(--text2);
  vertical-align: middle;
}
td code {
  font-family: 'Fira Code', monospace;
  font-size: 12px;
  background: var(--surface2);
  padding: 2px 7px;
  border-radius: 5px;
  color: var(--accent2);
  border: 1px solid var(--border);
}
td.good { color: var(--good); font-weight: 700; }
td.ok   { color: var(--ok);   font-weight: 700; }
td.bad  { color: var(--bad);  font-weight: 700; }

/* ── Callouts ── */
.callout {
  border-radius: var(--radius-sm);
  padding: 14px 16px;
  margin: 12px 0;
  border-left: 3px solid;
  font-size: 13px;
  line-height: 1.6;
}
.callout-title {
  font-size: 12px;
  font-weight: 700;
  letter-spacing: 0.3px;
  margin-bottom: 5px;
  display: flex;
  align-items: center;
  gap: 7px;
}
.callout.info    { background: rgba(96,165,250,0.07);  border-color: #60a5fa; color: var(--text2); }
.callout.info .callout-title { color: #60a5fa; }
.callout.success { background: rgba(52,211,153,0.07);  border-color: #34d399; color: var(--text2); }
.callout.success .callout-title { color: #34d399; }
.callout.warn    { background: rgba(251,191,36,0.07);  border-color: #fbbf24; color: var(--text2); }
.callout.warn .callout-title { color: #fbbf24; }
.callout.tip     { background: rgba(192,132,252,0.07); border-color: #c084fc; color: var(--text2); }
.callout.tip .callout-title { color: #c084fc; }

/* ── Buttons ── */
.btn {
  display: inline-flex;
  align-items: center;
  gap: 7px;
  padding: 9px 18px;
  border: none;
  border-radius: var(--radius-sm);
  font-size: 13px;
  font-weight: 600;
  font-family: 'Inter', sans-serif;
  cursor: pointer;
  transition: all 0.2s;
  white-space: nowrap;
  text-decoration: none;
}
.btn-primary  { background: var(--accent); color: #fff; box-shadow: 0 4px 14px rgba(108,99,255,0.3); }
.btn-primary:hover  { background: #7c74ff; transform: translateY(-1px); box-shadow: 0 6px 18px rgba(108,99,255,0.4); }
.btn-secondary{ background: var(--surface2); color: var(--text2); border: 1px solid var(--border); }
.btn-secondary:hover{ color: var(--text); border-color: var(--accent); transform: translateY(-1px); }
.btn-danger   { background: rgba(248,113,113,0.15); color: var(--bad); border: 1px solid rgba(248,113,113,0.3); }
.btn-danger:hover { background: rgba(248,113,113,0.25); transform: translateY(-1px); }

/* ── Problem List ── */
.problem-list { list-style: none; display: flex; flex-direction: column; gap: 8px; }
.problem-item {
  display: flex;
  align-items: center;
  gap: 12px;
  padding: 12px 16px;
  background: var(--surface2);
  border: 1px solid var(--border);
  border-radius: var(--radius-sm);
  transition: border-color 0.2s;
  flex-wrap: wrap;
}
.problem-item:hover { border-color: var(--accent); }

.problem-diff {
  font-size: 11px;
  font-weight: 700;
  padding: 3px 9px;
  border-radius: 20px;
  white-space: nowrap;
  flex-shrink: 0;
}
.problem-diff.easy   { background: rgba(52,211,153,0.15);  color: #34d399; }
.problem-diff.medium { background: rgba(251,191,36,0.15);  color: #fbbf24; }
.problem-diff.hard   { background: rgba(248,113,113,0.15); color: #f87171; }

.problem-name {
  flex: 1;
  font-size: 13px;
  font-weight: 600;
  color: var(--text);
  min-width: 150px;
}
.problem-pattern {
  font-size: 12px;
  color: var(--text3);
  font-family: 'Fira Code', monospace;
}

/* ── When To Use Box ── */
.when-to-use {
  background: rgba(108,99,255,0.07);
  border: 1px solid rgba(108,99,255,0.2);
  border-radius: var(--radius-sm);
  padding: 14px 16px;
  margin: 12px 0;
}
.wtu-title {
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.5px;
  color: var(--accent2);
  margin-bottom: 8px;
  display: flex;
  align-items: center;
  gap: 7px;
  text-transform: uppercase;
}
.when-to-use ul { padding-left: 18px; }
.when-to-use li { font-size: 13px; color: var(--text2); margin-bottom: 4px; }

/* ── Inline Code ── */
code {
  font-family: 'Fira Code', monospace;
  font-size: 12px;
  background: var(--surface2);
  padding: 2px 7px;
  border-radius: 5px;
  color: var(--accent2);
  border: 1px solid var(--border);
}

/* ── Scrollbar ── */
::-webkit-scrollbar { width: 6px; height: 6px; }
::-webkit-scrollbar-track { background: transparent; }
::-webkit-scrollbar-thumb { background: rgba(255,255,255,0.1); border-radius: 3px; }
::-webkit-scrollbar-thumb:hover { background: rgba(255,255,255,0.2); }

/* ── Responsive ── */
@media (max-width: 480px) {
  .page-hero { padding: 32px 16px 24px; }
  .page-main { padding: 20px 12px 60px; }
  .card { padding: 18px 14px; }
  .viz-body { padding: 14px; }
  .tab-btn { padding: 8px 12px; font-size: 12px; }
  .arr-cell { min-width: 38px; height: 44px; font-size: 13px; }
  pre { font-size: 12px; padding: 14px; }
}