/* ═══════════════════════════════════════════════════════════════════════════
   VisualizedAlgorithms — Custom Design System
   Phase 1: UI Shell
   ═══════════════════════════════════════════════════════════════════════════ */

/* ─── RESET ─────────────────────────────────────────────────────────────────── */
*,
*::before,
*::after {
  box-sizing: border-box;
  margin: 0;
  padding: 0;
}
button,
input {
  font-family: inherit;
}

/* ─── DESIGN TOKENS ──────────────────────────────────────────────────────────── */
:root {
  --vs-bg: #08080f;
  --vs-surface: #0f0f1e;
  --vs-card: #16162a;
  --vs-card-hover: #1c1c38;
  --vs-border: #252545;
  --vs-border-light: #2e2e55;

  --vs-blue: #5b8af7;
  --vs-violet: #8b5cf6;
  --vs-gradient: linear-gradient(135deg, #5b8af7 0%, #8b5cf6 100%);
  --vs-gradient-sub: linear-gradient(
    135deg,
    rgba(91, 138, 247, 0.12) 0%,
    rgba(139, 92, 246, 0.12) 100%
  );
  --vs-glow-blue: rgba(91, 138, 247, 0.3);

  --vs-text: #e8e8f5;
  --vs-text-2: #9898bb;
  --vs-text-3: #555570;

  --vs-bar-default: #3d3d6e;
  --vs-bar-compare: #f5c842;
  --vs-bar-swap: #f05454;
  --vs-bar-sorted: #42d97a;

  --vs-font: "Inter", -apple-system, BlinkMacSystemFont, sans-serif;
  --vs-mono: "JetBrains Mono", "Fira Code", "Cascadia Code", monospace;

  --vs-radius: 12px;
  --vs-radius-sm: 8px;
  --vs-radius-xs: 6px;
}

/* ─── BASE ───────────────────────────────────────────────────────────────────── */
html {
  font-family: var(--vs-font);
  background: var(--vs-bg);
  color: var(--vs-text);
  scroll-behavior: smooth;
  font-size: 16px;
}
body {
  min-height: 100vh;
  overflow-x: hidden;
}

::-webkit-scrollbar {
  width: 5px;
}
::-webkit-scrollbar-track {
  background: var(--vs-bg);
}
::-webkit-scrollbar-thumb {
  background: var(--vs-border-light);
  border-radius: 3px;
}

/* ─── UTILITY ────────────────────────────────────────────────────────────────── */
.vs-container {
  width: 100%;
  max-width: 1280px;
  margin: 0 auto;
  padding: 0 1rem;
}
.vs-hidden {
  display: none !important;
}

.vs-gradient-text {
  background: var(--vs-gradient);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}

/* ─── EYEBROW ────────────────────────────────────────────────────────────────── */
.vs-eyebrow {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  font-size: 0.7rem;
  font-weight: 600;
  letter-spacing: 0.14em;
  color: var(--vs-blue);
  margin-bottom: 1.25rem;
}
.vs-eyebrow-dot {
  width: 6px;
  height: 6px;
  background: var(--vs-blue);
  border-radius: 50%;
  box-shadow: 0 0 8px var(--vs-blue);
  animation: vs-dot-pulse 2.2s ease-in-out infinite;
}
@keyframes vs-dot-pulse {
  0%,
  100% {
    opacity: 1;
    transform: scale(1);
  }
  50% {
    opacity: 0.4;
    transform: scale(0.65);
  }
}

/* ─── NAVBAR ─────────────────────────────────────────────────────────────────── */
.vs-nav {
  position: sticky;
  top: 0;
  z-index: 200;
  background: rgba(8, 8, 15, 0.88);
  backdrop-filter: blur(20px);
  -webkit-backdrop-filter: blur(20px);
  border-bottom: 1px solid var(--vs-border);
}
.vs-nav-inner {
  max-width: 1280px;
  margin: 0 auto;
  padding: 0 1rem;
  min-height: 64px;
  display: flex;
  align-items: center;
  justify-content: space-between;
  position: relative;
  gap: 1rem;
}
.vs-nav-logo {
  font-size: clamp(0.9rem, 4vw, 1.05rem);
  font-weight: 700;
  letter-spacing: -0.025em;
  color: var(--vs-text);
  text-decoration: none;
  min-width: 0;
}
.logo-bracket {
  background: var(--vs-gradient);
  -webkit-background-clip: text;
  -webkit-text-fill-color: transparent;
  background-clip: text;
}
.vs-nav-toggle {
  width: 42px;
  height: 42px;
  display: inline-flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 5px;
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-xs);
  color: var(--vs-text);
  cursor: pointer;
}
.vs-nav-toggle span {
  width: 18px;
  height: 2px;
  border-radius: 999px;
  background: currentColor;
  transition:
    transform 0.2s,
    opacity 0.2s;
}
.vs-nav-open .vs-nav-toggle span:nth-child(1) {
  transform: translateY(7px) rotate(45deg);
}
.vs-nav-open .vs-nav-toggle span:nth-child(2) {
  opacity: 0;
}
.vs-nav-open .vs-nav-toggle span:nth-child(3) {
  transform: translateY(-7px) rotate(-45deg);
}
.vs-nav-links {
  position: absolute;
  top: calc(100% - 1px);
  left: 1rem;
  right: 1rem;
  display: grid;
  grid-template-columns: 1fr;
  gap: 0.35rem;
  max-height: 0;
  overflow: hidden;
  padding: 0;
  background: rgba(15, 15, 30, 0.98);
  border: 0 solid var(--vs-border);
  border-radius: 0 0 var(--vs-radius-sm) var(--vs-radius-sm);
  box-shadow: 0 22px 50px rgba(0, 0, 0, 0.35);
  transition:
    max-height 0.25s ease,
    padding 0.25s ease,
    border-width 0.25s ease;
}
.vs-nav-open .vs-nav-links {
  max-height: calc(100vh - 64px);
  overflow-y: auto;
  padding: 0.75rem;
  border-width: 1px;
}
.vs-nav-link {
  color: var(--vs-text-2);
  text-decoration: none;
  font-size: 0.9rem;
  font-weight: 500;
  padding: 0.65rem 0.75rem;
  border-radius: var(--vs-radius-xs);
  transition: color 0.2s;
}
.vs-nav-link:hover {
  color: var(--vs-text);
}
.vs-nav-link-active {
  color: var(--vs-text);
  background: rgba(91, 138, 247, 0.12);
  border: 1px solid rgba(91, 138, 247, 0.25);
  border-radius: var(--vs-radius-xs);
  padding: 0.65rem 0.75rem;
}
.vs-nav-cta {
  background: var(--vs-gradient);
  color: #fff;
  text-decoration: none;
  font-size: 0.825rem;
  font-weight: 600;
  padding: 0.65rem 0.9rem;
  border-radius: var(--vs-radius-xs);
  text-align: center;
  transition:
    opacity 0.2s,
    transform 0.2s;
}
.vs-nav-cta:hover {
  opacity: 0.85;
  transform: translateY(-1px);
}

/* ─── HERO ───────────────────────────────────────────────────────────────────── */
.vs-hero {
  position: relative;
  min-height: auto;
  display: flex;
  align-items: center;
  overflow: hidden;
}
.vs-hero-grid-bg {
  position: absolute;
  inset: 0;
  pointer-events: none;
  z-index: 0;
  background-image:
    linear-gradient(rgba(91, 138, 247, 0.045) 1px, transparent 1px),
    linear-gradient(90deg, rgba(91, 138, 247, 0.045) 1px, transparent 1px);
  background-size: 56px 56px;
  mask-image: radial-gradient(
    ellipse 90% 85% at 50% 40%,
    black 20%,
    transparent 80%
  );
  -webkit-mask-image: radial-gradient(
    ellipse 90% 85% at 50% 40%,
    black 20%,
    transparent 80%
  );
}
.vs-hero-inner {
  position: relative;
  z-index: 1;
  display: grid;
  grid-template-columns: 1fr;
  gap: 2rem;
  align-items: center;
  padding: 3rem 0 2rem;
}
.vs-welcome-hero .vs-hero-inner {
  grid-template-columns: 1fr;
  padding-bottom: 2rem;
}
.vs-home-hero-visual {
  align-self: center;
}

/* Hero text */
.vs-hero-title {
  font-size: clamp(2.25rem, 12vw, 3.6rem);
  font-weight: 900;
  line-height: 1.04;
  letter-spacing: -0.045em;
  color: var(--vs-text);
  margin-bottom: 1.5rem;
}
.vs-hero-subtitle {
  font-size: 1rem;
  font-weight: 400;
  line-height: 1.7;
  color: var(--vs-text-2);
  margin-bottom: 2.5rem;
}
.vs-hero-actions {
  display: flex;
  flex-direction: column;
  gap: 2rem;
}
.vs-home-actions {
  position: relative;
  z-index: 1;
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
  padding-bottom: 3rem;
}
.vs-home-card {
  display: flex;
  min-height: 180px;
  flex-direction: column;
  justify-content: space-between;
  gap: 1rem;
  padding: 1.25rem;
  color: var(--vs-text);
  text-decoration: none;
  background: var(--vs-card);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-sm);
  transition:
    transform 0.2s,
    border-color 0.2s,
    background 0.2s;
}
.vs-home-card:hover {
  transform: translateY(-3px);
  border-color: rgba(91, 138, 247, 0.55);
  background: var(--vs-card-hover);
}
.vs-home-card-kicker {
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
  color: var(--vs-blue);
}
.vs-home-card strong {
  display: block;
  font-size: 1.55rem;
  line-height: 1.1;
}
.vs-home-card span:last-child {
  color: var(--vs-text-2);
  font-size: 0.9rem;
  line-height: 1.55;
}
.vs-welcome-panel {
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius);
  padding: 1.25rem;
  display: grid;
  gap: 0.9rem;
}
.vs-welcome-panel-row {
  background: rgba(255, 255, 255, 0.025);
  border: 1px solid rgba(255, 255, 255, 0.055);
  border-radius: var(--vs-radius-sm);
  padding: 1.1rem;
}
.vs-welcome-panel-row span {
  display: block;
  margin-bottom: 0.5rem;
  color: var(--vs-blue);
  font-size: 0.68rem;
  font-weight: 700;
  letter-spacing: 0.1em;
  text-transform: uppercase;
}
.vs-welcome-panel-row strong {
  display: block;
  color: var(--vs-text);
  font-size: 1.1rem;
  line-height: 1.45;
}

.vs-btn-primary {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: var(--vs-gradient);
  color: #fff;
  text-decoration: none;
  font-size: 0.95rem;
  font-weight: 600;
  padding: 0.875rem 2rem;
  border-radius: var(--vs-radius-sm);
  width: fit-content;
  box-shadow: 0 4px 28px var(--vs-glow-blue);
  transition:
    transform 0.2s,
    box-shadow 0.2s;
}
.vs-btn-primary:hover {
  transform: translateY(-3px);
  box-shadow: 0 10px 36px var(--vs-glow-blue);
}

.vs-hero-stats {
  display: flex;
  align-items: center;
  gap: 1.75rem;
}
.vs-stat {
  display: flex;
  flex-direction: column;
  gap: 0.1rem;
}
.vs-stat-num {
  font-size: 1.6rem;
  font-weight: 800;
  color: var(--vs-text);
  line-height: 1;
}
.vs-stat-label {
  font-size: 0.68rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--vs-text-3);
}
.vs-stat-divider {
  width: 1px;
  height: 2.2rem;
  background: var(--vs-border);
}

/* Hero visual widget */
.vs-hero-visual {
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: 16px;
  padding: 1.25rem;
  position: relative;
  overflow: hidden;
  transition: border-color 0.3s;
}
.vs-hero-visual:hover {
  border-color: rgba(91, 138, 247, 0.45);
}

.vs-hero-visual::after {
  content: "";
  position: absolute;
  inset: 0;
  border-radius: 16px;
  background: radial-gradient(
    ellipse 80% 60% at 50% 0%,
    rgba(91, 138, 247, 0.07),
    transparent 70%
  );
  pointer-events: none;
}

.vs-hero-visual-topbar {
  display: flex;
  align-items: center;
  justify-content: space-between;
  padding-bottom: 0.875rem;
  border-bottom: 1px solid var(--vs-border);
  margin-bottom: 0.875rem;
}
.vs-hero-visual-label {
  font-family: var(--vs-mono);
  font-size: 0.72rem;
  color: var(--vs-text-3);
}
.vs-hero-visual-status {
  font-size: 0.68rem;
  font-weight: 600;
  letter-spacing: 0.06em;
  color: var(--vs-bar-compare);
  animation: vs-status-blink 1.4s ease-in-out infinite;
}
@keyframes vs-status-blink {
  0%,
  100% {
    opacity: 1;
  }
  50% {
    opacity: 0.3;
  }
}

.vs-hero-bars-wrap {
  display: flex;
  align-items: flex-end;
  height: clamp(150px, 42vw, 190px);
  padding: 0 0.25rem;
}
.vs-hero-bars {
  display: flex;
  align-items: flex-end;
  gap: 4px;
  width: 100%;
  height: 100%;
}

/* Individual hero bars */
.vs-hero-bar {
  flex: 1;
  min-width: 0;
  border-radius: 3px 3px 0 0;
  transform-origin: bottom;
  animation: vs-bar-dance var(--dur, 2s) var(--delay, 0s) ease-in-out infinite
    alternate;
}
@keyframes vs-bar-dance {
  from {
    transform: scaleY(1);
  }
  to {
    transform: scaleY(var(--to, 0.45));
  }
}
.vs-bar-default {
  background: var(--vs-bar-default);
}
.vs-bar-compare {
  background: var(--vs-bar-compare);
  box-shadow: 0 0 10px rgba(245, 200, 66, 0.55);
}
.vs-bar-swap {
  background: var(--vs-bar-swap);
  box-shadow: 0 0 10px rgba(240, 84, 84, 0.5);
}
.vs-bar-sorted {
  background: linear-gradient(180deg, #42d97a 0%, #2ab862 100%);
  box-shadow: 0 0 8px rgba(66, 217, 122, 0.3);
}

/* Legend */
.vs-hero-visual-legend {
  display: flex;
  align-items: center;
  gap: 1.1rem;
  flex-wrap: wrap;
  padding-top: 0.875rem;
  border-top: 1px solid var(--vs-border);
  margin-top: 0.875rem;
}
.vs-legend-item {
  display: inline-flex;
  align-items: center;
  gap: 0.3rem;
  font-size: 0.7rem;
  color: var(--vs-text-3);
}
.vs-legend-dot {
  width: 8px;
  height: 8px;
  border-radius: 2px;
  flex-shrink: 0;
}
.vs-dot-default {
  background: var(--vs-bar-default);
}
.vs-dot-compare {
  background: var(--vs-bar-compare);
}
.vs-dot-swap {
  background: var(--vs-bar-swap);
}
.vs-dot-sorted {
  background: var(--vs-bar-sorted);
}

/* ─── ALGORITHMS SECTION ─────────────────────────────────────────────────────── */
.vs-algos-section {
  padding: 3.5rem 0;
}
.vs-page-head {
  padding-top: 2.5rem;
}

.vs-section-header {
  text-align: center;
  margin-bottom: 2.5rem;
}
.vs-section-title {
  font-size: clamp(1.9rem, 3vw, 2.6rem);
  font-weight: 800;
  letter-spacing: -0.035em;
  margin-bottom: 0.875rem;
  margin-top: 0.75rem;
}
.vs-section-subtitle {
  font-size: 1rem;
  line-height: 1.75;
  color: var(--vs-text-2);
  max-width: 540px;
  margin: 0 auto;
}

/* Algorithm card grid */
.vs-algo-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
}

.vs-algo-card {
  background: var(--vs-card);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius);
  padding: 1.2rem;
  cursor: pointer;
  position: relative;
  overflow: hidden;
  transition:
    transform 0.25s,
    background 0.25s,
    border-color 0.25s,
    box-shadow 0.25s;
}
.vs-algo-card::before {
  content: "";
  position: absolute;
  inset: 0;
  background: var(--vs-gradient-sub);
  opacity: 0;
  transition: opacity 0.25s;
  border-radius: var(--vs-radius);
}
.vs-algo-card:hover {
  transform: translateY(-5px);
  background: var(--vs-card-hover);
  border-color: rgba(91, 138, 247, 0.55);
  box-shadow: 0 10px 44px rgba(91, 138, 247, 0.12);
}
.vs-algo-card:hover::before {
  opacity: 1;
}

.vs-algo-card-header {
  display: flex;
  align-items: flex-start;
  justify-content: space-between;
  gap: 0.75rem;
  flex-wrap: wrap;
  margin-bottom: 1.25rem;
}
.vs-algo-name {
  font-size: 1.075rem;
  font-weight: 700;
  letter-spacing: -0.02em;
  line-height: 1.2;
}

/* Category badges */
.vs-category-badge {
  font-size: 0.62rem;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  padding: 0.25rem 0.65rem;
  border-radius: 20px;
  white-space: normal;
  flex-shrink: 0;
  max-width: 100%;
}
.vs-badge-comparison {
  background: rgba(91, 138, 247, 0.13);
  color: var(--vs-blue);
  border: 1px solid rgba(91, 138, 247, 0.3);
}
.vs-badge-noncomparison {
  background: rgba(139, 92, 246, 0.13);
  color: var(--vs-violet);
  border: 1px solid rgba(139, 92, 246, 0.3);
}
.vs-badge-tree {
  background: rgba(66, 217, 122, 0.12);
  color: var(--vs-bar-sorted);
  border: 1px solid rgba(66, 217, 122, 0.28);
}
.vs-badge-graph {
  background: rgba(245, 200, 66, 0.12);
  color: var(--vs-bar-compare);
  border: 1px solid rgba(245, 200, 66, 0.28);
}
.vs-badge-dp {
  background: rgba(139, 92, 246, 0.13);
  color: var(--vs-violet);
  border: 1px solid rgba(139, 92, 246, 0.32);
}
.vs-badge-greedy {
  background: rgba(240, 84, 84, 0.12);
  color: #f07070;
  border: 1px solid rgba(240, 84, 84, 0.3);
}
.vs-badge-topic {
  background: rgba(91, 138, 247, 0.12);
  color: var(--vs-blue);
  border: 1px solid rgba(91, 138, 247, 0.3);
}

/* Complexity table */
.vs-complexity-table {
  width: 100%;
  border-collapse: collapse;
  margin-bottom: 1.25rem;
}
.vs-complexity-table td {
  padding: 0.375rem 0;
  font-size: 0.8rem;
  border-bottom: 1px solid rgba(255, 255, 255, 0.04);
}
.vs-complexity-table tr:last-child td {
  border-bottom: none;
}
.vs-complexity-table td:first-child {
  color: var(--vs-text-3);
  font-weight: 500;
  width: 55%;
}
.vs-complexity-table td:last-child {
  font-family: var(--vs-mono);
  font-size: 0.77rem;
  font-weight: 500;
  color: var(--vs-text);
}

.vs-card-footer {
  display: flex;
  align-items: center;
  justify-content: flex-end;
  gap: 0.35rem;
  font-size: 0.8rem;
  font-weight: 600;
  color: var(--vs-blue);
  opacity: 0;
  transform: translateX(-6px);
  transition:
    opacity 0.25s,
    transform 0.25s;
}
.vs-algo-card:hover .vs-card-footer {
  opacity: 1;
  transform: translateX(0);
}

/* ─── VISUALIZER SECTION ─────────────────────────────────────────────────────── */
.vs-viz-section {
  padding: 1.5rem 0 4rem;
}

.vs-back-btn {
  display: inline-flex;
  align-items: center;
  gap: 0.5rem;
  background: transparent;
  border: 1px solid var(--vs-border);
  color: var(--vs-text-2);
  font-size: 0.85rem;
  font-weight: 500;
  padding: 0.5rem 1.1rem;
  border-radius: var(--vs-radius-xs);
  cursor: pointer;
  margin-bottom: 2rem;
  transition:
    border-color 0.2s,
    color 0.2s;
}
.vs-back-btn:hover {
  border-color: var(--vs-blue);
  color: var(--vs-text);
}

.vs-viz-inner {
  display: grid;
  grid-template-columns: 1fr;
  gap: 1rem;
  align-items: start;
  min-width: 0;
}

/* ─── VIZ MAIN (left pane) ───────────────────────────────────────────────────── */
.vs-viz-main {
  background: var(--vs-card);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius);
  padding: 1rem;
  display: flex;
  flex-direction: column;
  gap: 1.1rem;
  min-width: 0;
}
.vs-viz-header {
  display: flex;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}
.vs-viz-title {
  font-size: clamp(1.2rem, 6vw, 1.5rem);
  font-weight: 800;
  letter-spacing: -0.03em;
}
.vs-color-legend {
  display: flex;
  align-items: center;
  gap: 1.25rem;
  flex-wrap: wrap;
}

/* Bar chart */
.vs-bars-container {
  height: clamp(220px, 64vw, 300px);
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-sm);
  display: flex;
  align-items: flex-end;
  padding: 0.9rem 0.75rem 0;
  gap: 2px;
  overflow: hidden;
}
.vs-bar {
  flex: 1;
  min-width: 2px;
  border-radius: 2px 2px 0 0;
  background: var(--vs-bar-default);
  transition:
    height 0.06s linear,
    background 0.08s;
}
.vs-bar.vs-state-compare {
  background: var(--vs-bar-compare);
  box-shadow: 0 0 7px rgba(245, 200, 66, 0.5);
}
.vs-bar.vs-state-swap {
  background: var(--vs-bar-swap);
  box-shadow: 0 0 7px rgba(240, 84, 84, 0.5);
}
.vs-bar.vs-state-sorted {
  background: var(--vs-bar-sorted);
}

/* Tree visualizer */
.vs-tree-stage {
  min-height: clamp(260px, 72vw, 380px);
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-sm);
  overflow: hidden;
}
.vs-tree-stage svg {
  display: block;
  max-width: 100%;
  height: auto;
}
.vs-tree-edge {
  stroke: var(--vs-border-light);
  stroke-width: 2;
}
.vs-tree-node circle,
.vs-tree-node rect {
  fill: #202044;
  stroke: var(--vs-border-light);
  stroke-width: 2;
}
.vs-tree-node text {
  fill: var(--vs-text);
  font-family: var(--vs-mono);
  font-size: 13px;
  font-weight: 700;
  text-anchor: middle;
  dominant-baseline: middle;
}
.vs-tree-node-visit circle,
.vs-tree-node-visit rect {
  fill: rgba(245, 200, 66, 0.22);
  stroke: var(--vs-bar-compare);
}
.vs-tree-node-change circle,
.vs-tree-node-change rect {
  fill: rgba(240, 84, 84, 0.2);
  stroke: var(--vs-bar-swap);
}
.vs-tree-node-found circle,
.vs-tree-node-found rect {
  fill: rgba(66, 217, 122, 0.18);
  stroke: var(--vs-bar-sorted);
}
.vs-tree-controls {
  display: grid;
  gap: 1rem;
}
.vs-tree-input-row {
  display: flex;
  gap: 0.75rem;
  flex-wrap: wrap;
}
.vs-tree-input {
  width: min(110px, 100%);
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: 7px;
  color: var(--vs-text);
  font-family: var(--vs-mono);
  font-size: 0.9rem;
  padding: 0.625rem 0.75rem;
  outline: none;
}
.vs-tree-input:focus {
  border-color: var(--vs-blue);
}
.vs-tree-speed {
  min-width: 0;
  flex: 1;
}
.vs-tree-log {
  margin: 0;
  padding-left: 1.1rem;
  color: var(--vs-text-2);
  font-size: 0.8rem;
  line-height: 1.7;
}
.vs-tree-log li::marker {
  color: var(--vs-blue);
  font-family: var(--vs-mono);
}

/* Graph visualizer */
.vs-graph-stage {
  min-height: clamp(280px, 76vw, 430px);
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-sm);
  overflow: hidden;
}
.vs-graph-stage svg {
  display: block;
  max-width: 100%;
  height: auto;
}
.vs-graph-edge {
  stroke: var(--vs-border-light);
  stroke-width: 2.5;
}
.vs-graph-edge-frontier {
  stroke: var(--vs-bar-compare);
  stroke-width: 4;
}
.vs-graph-edge-path,
.vs-graph-edge-mst {
  stroke: var(--vs-bar-sorted);
  stroke-width: 4;
}
.vs-graph-edge-rejected {
  stroke: var(--vs-bar-swap);
  stroke-width: 4;
  stroke-dasharray: 8 5;
}
.vs-graph-weight {
  fill: var(--vs-text-2);
  font-family: var(--vs-mono);
  font-size: 12px;
  font-weight: 700;
  paint-order: stroke;
  stroke: var(--vs-surface);
  stroke-width: 4;
}
.vs-graph-node circle {
  fill: #202044;
  stroke: var(--vs-border-light);
  stroke-width: 2;
}
.vs-graph-node text {
  fill: var(--vs-text);
  font-family: var(--vs-mono);
  font-size: 14px;
  font-weight: 800;
  text-anchor: middle;
  dominant-baseline: middle;
}
.vs-graph-node-frontier circle {
  fill: rgba(245, 200, 66, 0.22);
  stroke: var(--vs-bar-compare);
}
.vs-graph-node-current circle {
  fill: rgba(240, 84, 84, 0.2);
  stroke: var(--vs-bar-swap);
}
.vs-graph-node-visited circle,
.vs-graph-node-path circle {
  fill: rgba(66, 217, 122, 0.18);
  stroke: var(--vs-bar-sorted);
}
.vs-select-label {
  display: inline-flex;
  align-items: center;
  gap: 0.55rem;
  flex-wrap: wrap;
  color: var(--vs-text-2);
  font-size: 0.8rem;
  font-weight: 600;
}
.vs-select {
  max-width: 100%;
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: 7px;
  color: var(--vs-text);
  font-family: var(--vs-mono);
  padding: 0.625rem 0.75rem;
  outline: none;
}
.vs-select:focus {
  border-color: var(--vs-blue);
}

/* Dynamic programming visualizer */
.vs-dp-stage {
  min-height: clamp(260px, 72vw, 380px);
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-sm);
  overflow: auto;
  padding: 0.75rem;
  --vs-dp-cell-min: 42px;
}
.vs-dp-table {
  display: grid;
  gap: 4px;
  width: max-content;
  min-width: 100%;
}
.vs-dp-cell {
  min-width: var(--vs-dp-cell-min);
  min-height: 38px;
  height: auto;
  padding: 0.4rem 0.45rem;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #202044;
  border: 1px solid var(--vs-border-light);
  border-radius: 6px;
  color: var(--vs-text);
  font-family: var(--vs-mono);
  font-size: clamp(0.68rem, 3vw, 0.78rem);
  font-weight: 700;
  overflow-wrap: anywhere;
  text-align: center;
}
.vs-dp-cell-label {
  background: transparent;
  border-color: transparent;
  color: var(--vs-text-3);
  font-size: 0.7rem;
  text-transform: uppercase;
}
.vs-dp-cell-read {
  background: rgba(245, 200, 66, 0.18);
  border-color: var(--vs-bar-compare);
}
.vs-dp-cell-write {
  background: rgba(240, 84, 84, 0.16);
  border-color: var(--vs-bar-swap);
}
.vs-dp-cell-done {
  background: rgba(66, 217, 122, 0.16);
  border-color: rgba(66, 217, 122, 0.5);
}
.vs-dp-caption {
  margin-top: 0.85rem;
  color: var(--vs-text-2);
  font-size: 0.85rem;
  line-height: 1.55;
}

/* Greedy visualizer */
.vs-greedy-stage {
  min-height: clamp(260px, 72vw, 380px);
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-sm);
  overflow: auto;
  padding: 0.75rem;
}
.vs-greedy-list {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(145px, 100%), 1fr));
  gap: 0.75rem;
}
.vs-greedy-item {
  min-height: 96px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  gap: 0.65rem;
  background: #202044;
  border: 1px solid var(--vs-border-light);
  border-radius: var(--vs-radius-sm);
  padding: 0.9rem;
  transition:
    border-color 0.15s,
    background 0.15s;
}
.vs-greedy-item-title {
  color: var(--vs-text);
  font-weight: 800;
  line-height: 1.25;
}
.vs-greedy-item-meta {
  color: var(--vs-text-2);
  font-family: var(--vs-mono);
  font-size: 0.74rem;
  line-height: 1.45;
}
.vs-greedy-item-consider {
  background: rgba(245, 200, 66, 0.18);
  border-color: var(--vs-bar-compare);
}
.vs-greedy-item-reject {
  background: rgba(240, 84, 84, 0.16);
  border-color: var(--vs-bar-swap);
}
.vs-greedy-item-chosen {
  background: rgba(66, 217, 122, 0.16);
  border-color: rgba(66, 217, 122, 0.55);
}
.vs-greedy-item-muted {
  opacity: 0.58;
}
.vs-greedy-caption {
  margin-top: 0.9rem;
  color: var(--vs-text-2);
  font-size: 0.85rem;
  line-height: 1.55;
}

/* Shared textbook-section visualizer */
.vs-topic-stage {
  min-height: clamp(260px, 72vw, 380px);
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-sm);
  overflow: auto;
  padding: 0.75rem;
}
.vs-topic-list {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(136px, 100%), 1fr));
  gap: 0.75rem;
}
.vs-topic-item {
  min-height: 92px;
  display: flex;
  flex-direction: column;
  justify-content: space-between;
  gap: 0.6rem;
  background: #202044;
  border: 1px solid var(--vs-border-light);
  border-radius: var(--vs-radius-sm);
  padding: 0.85rem;
}
.vs-topic-title {
  color: var(--vs-text);
  font-weight: 800;
  line-height: 1.25;
}
.vs-topic-meta {
  color: var(--vs-text-2);
  font-family: var(--vs-mono);
  font-size: 0.73rem;
  line-height: 1.45;
}
.vs-topic-item-active {
  background: rgba(245, 200, 66, 0.18);
  border-color: var(--vs-bar-compare);
}
.vs-topic-item-bad {
  background: rgba(240, 84, 84, 0.16);
  border-color: var(--vs-bar-swap);
}
.vs-topic-item-good {
  background: rgba(66, 217, 122, 0.16);
  border-color: rgba(66, 217, 122, 0.55);
}
.vs-topic-item-muted {
  opacity: 0.6;
}
.vs-topic-caption {
  margin-top: 0.9rem;
  color: var(--vs-text-2);
  font-size: 0.85rem;
  line-height: 1.55;
}

/* Stats row */
.vs-stats-row {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(min(96px, 100%), 1fr));
  gap: 0.75rem;
}
.vs-stat-box {
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-sm);
  padding: 1rem;
  text-align: center;
}
.vs-stat-box-num {
  display: block;
  font-size: clamp(1.05rem, 5vw, 1.5rem);
  font-weight: 800;
  font-family: var(--vs-mono);
  color: var(--vs-text);
  line-height: 1.15;
  margin-bottom: 0.375rem;
  overflow-wrap: anywhere;
}
.vs-stat-box-label {
  font-size: 0.67rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--vs-text-3);
}

/* Controls */
.vs-controls {
  display: flex;
  flex-direction: column;
  gap: 1rem;
  align-items: stretch;
}
.vs-input-panel {
  display: grid;
  gap: 0.85rem;
  padding: 0.9rem;
  background: rgba(255, 255, 255, 0.025);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-sm);
}
.vs-input-grid {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  gap: 0.75rem;
}
.vs-input-label {
  display: grid;
  gap: 0.4rem;
  min-width: 0;
  color: var(--vs-text-2);
  font-size: 0.75rem;
  font-weight: 700;
  text-transform: uppercase;
  letter-spacing: 0.08em;
}
.vs-manual-input {
  width: 100%;
  min-width: 0;
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  border-radius: 7px;
  color: var(--vs-text);
  font-family: var(--vs-mono);
  font-size: 0.86rem;
  padding: 0.68rem 0.75rem;
  outline: none;
}
.vs-manual-input:focus {
  border-color: var(--vs-blue);
  box-shadow: 0 0 0 3px rgba(91, 138, 247, 0.12);
}
.vs-input-actions {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.6rem;
}
.vs-input-error {
  min-height: 1.15rem;
  margin: 0;
  color: var(--vs-bar-swap);
  font-size: 0.8rem;
  line-height: 1.45;
}
.vs-ctrl-btns {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 0.6rem;
  align-items: stretch;
}

.vs-ctrl-btn {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  gap: 0.4rem;
  background: var(--vs-surface);
  border: 1px solid var(--vs-border);
  color: var(--vs-text-2);
  font-size: 0.85rem;
  font-weight: 500;
  padding: 0.7rem 0.75rem;
  border-radius: 7px;
  cursor: pointer;
  min-width: 0;
  transition:
    border-color 0.2s,
    color 0.2s,
    transform 0.15s;
}
.vs-ctrl-btn:hover {
  border-color: var(--vs-border-light);
  color: var(--vs-text);
  transform: translateY(-1px);
}
.vs-ctrl-btn:active {
  transform: translateY(0);
}

.vs-ctrl-btn-primary {
  background: var(--vs-gradient);
  border-color: transparent;
  color: #fff;
  box-shadow: 0 2px 16px rgba(91, 138, 247, 0.25);
}
.vs-ctrl-btn-primary:hover {
  opacity: 0.88;
  box-shadow: 0 4px 24px rgba(91, 138, 247, 0.35);
}

.vs-sliders {
  display: flex;
  flex-direction: column;
  gap: 0.875rem;
  flex: 1;
  min-width: 0;
  width: 100%;
}

.vs-slider-label {
  display: grid;
  grid-template-columns: auto auto minmax(0, 1fr);
  align-items: center;
  gap: 0.75rem;
  font-size: 0.8rem;
  font-weight: 500;
  color: var(--vs-text-2);
}
.vs-slider-val {
  font-family: var(--vs-mono);
  font-size: 0.75rem;
  color: var(--vs-blue);
  min-width: 1.8rem;
  text-align: center;
}
.vs-slider {
  flex: 1;
  -webkit-appearance: none;
  appearance: none;
  height: 3px;
  background: var(--vs-border-light);
  border-radius: 2px;
  outline: none;
  cursor: pointer;
}
.vs-slider::-webkit-slider-thumb {
  -webkit-appearance: none;
  width: 14px;
  height: 14px;
  background: var(--vs-blue);
  border-radius: 50%;
  cursor: pointer;
  box-shadow: 0 0 6px rgba(91, 138, 247, 0.55);
  transition: transform 0.15s;
}
.vs-slider::-webkit-slider-thumb:hover {
  transform: scale(1.25);
}
.vs-slider::-moz-range-thumb {
  width: 14px;
  height: 14px;
  background: var(--vs-blue);
  border-radius: 50%;
  cursor: pointer;
  border: none;
  box-shadow: 0 0 6px rgba(91, 138, 247, 0.55);
}

/* ─── INFO PANEL (right pane) ────────────────────────────────────────────────── */
.vs-info-panel {
  display: flex;
  flex-direction: column;
  gap: 1.1rem;
  position: static;
  min-width: 0;
}
.vs-complexity-grid {
  display: grid;
  grid-template-columns: 1fr;
  gap: 0.75rem;
}
.vs-complexity-card {
  background: var(--vs-card);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-sm);
  padding: 0.875rem;
  display: flex;
  flex-direction: column;
  gap: 0.3rem;
}
.vs-complexity-label {
  font-size: 0.65rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.1em;
  color: var(--vs-text-3);
}
.vs-complexity-val {
  font-size: 0.925rem;
  font-weight: 700;
  font-family: var(--vs-mono);
  color: var(--vs-blue);
  line-height: 1.2;
  overflow-wrap: anywhere;
}
.vs-complexity-val-worst {
  color: #f07070 !important;
}

.vs-info-card {
  background: var(--vs-card);
  border: 1px solid var(--vs-border);
  border-radius: var(--vs-radius-sm);
  padding: 1.25rem;
}
.vs-info-card-title {
  font-size: 0.67rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--vs-text-3);
  margin-bottom: 0.75rem;
}
.vs-info-text {
  font-size: 0.875rem;
  line-height: 1.75;
  color: var(--vs-text-2);
}

/* Pseudocode */
.vs-pseudocode {
  font-family: var(--vs-mono);
  font-size: 0.76rem;
  line-height: 1.75;
  color: #c0c0e0;
  white-space: pre-wrap;
  overflow-wrap: anywhere;
  overflow-x: auto;
  margin: 0;
  scrollbar-width: thin;
  scrollbar-color: var(--vs-border) transparent;
}
.vs-pseudocode .vs-line-active {
  display: block;
  background: rgba(91, 138, 247, 0.14);
  border-left: 2px solid var(--vs-blue);
  padding-left: 0.5rem;
  margin-left: -0.5rem;
}

/* ─── FOOTER ─────────────────────────────────────────────────────────────────── */
.vs-footer {
  border-top: 1px solid var(--vs-border);
  padding: 1.75rem 0;
}
.vs-footer-inner {
  display: flex;
  align-items: center;
  justify-content: space-between;
  flex-wrap: wrap;
  gap: 1rem;
}
.vs-footer-logo {
  font-size: 0.9rem;
  font-weight: 700;
}
.vs-footer-tagline {
  font-size: 0.8rem;
  color: var(--vs-text-3);
}

/* ─── RESPONSIVE ─────────────────────────────────────────────────────────────── */
@media (min-width: 520px) {
  .vs-container {
    padding: 0 1.25rem;
  }
  .vs-home-actions {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
  .vs-complexity-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
  .vs-input-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
  .vs-input-actions {
    grid-template-columns: repeat(3, auto);
    justify-content: start;
  }
  .vs-controls {
    flex-direction: row;
    align-items: flex-start;
  }
  .vs-ctrl-btns {
    grid-template-columns: repeat(3, auto);
  }
  .vs-ctrl-btn {
    width: auto;
    padding: 0.625rem 1.1rem;
  }
  .vs-dp-stage {
    --vs-dp-cell-min: 48px;
  }
}

@media (min-width: 700px) {
  .vs-algo-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
    gap: 1.25rem;
  }
  .vs-algo-card {
    padding: 1.5rem;
  }
  .vs-viz-main {
    padding: 1.5rem;
    gap: 1.35rem;
  }
  .vs-bars-container {
    padding: 1.1rem 1rem 0;
  }
  .vs-dp-stage,
  .vs-greedy-stage,
  .vs-topic-stage {
    padding: 1rem;
  }
}

@media (min-width: 901px) {
  .vs-container {
    padding: 0 2rem;
  }
  .vs-nav-inner {
    padding: 0 2rem;
    height: 64px;
  }
  .vs-nav-toggle {
    display: none;
  }
  .vs-nav-links {
    position: static;
    display: flex;
    align-items: center;
    justify-content: flex-end;
    flex-wrap: wrap;
    gap: 0.9rem;
    max-height: none;
    overflow: visible;
    padding: 0;
    background: transparent;
    border: 0;
    border-radius: 0;
    box-shadow: none;
    transition: none;
  }
  .vs-nav-link {
    font-size: 0.82rem;
    padding: 0;
  }
  .vs-nav-link-active {
    padding: 0.45rem 0.85rem;
  }
  .vs-nav-cta {
    padding: 0.5rem 1.2rem;
  }

  .vs-hero {
    min-height: calc(100vh - 64px);
  }
  .vs-hero-inner {
    grid-template-columns: 1fr 1fr;
    gap: 4rem;
    padding: 5rem 0;
  }
  .vs-welcome-hero .vs-hero-inner {
    grid-template-columns: minmax(0, 0.95fr) minmax(320px, 1.05fr);
    padding-bottom: 2.25rem;
  }
  .vs-hero-title {
    font-size: clamp(2.8rem, 4.8vw, 4.6rem);
  }
  .vs-hero-subtitle {
    font-size: 1.075rem;
  }
  .vs-home-actions {
    grid-template-columns: repeat(auto-fit, minmax(210px, 1fr));
    padding-bottom: 5rem;
  }

  .vs-algos-section {
    padding: 6rem 0;
  }
  .vs-page-head {
    padding-top: 4rem;
  }
  .vs-section-header {
    margin-bottom: 4rem;
  }
  .vs-algo-grid {
    grid-template-columns: repeat(3, minmax(0, 1fr));
  }
  .vs-algo-card {
    padding: 1.75rem;
  }
  .vs-algo-card-header {
    flex-wrap: nowrap;
  }
  .vs-category-badge {
    white-space: nowrap;
  }

  .vs-viz-section {
    padding: 2rem 0 6rem;
  }
  .vs-viz-main {
    padding: 2rem;
    gap: 1.5rem;
  }
  .vs-bars-container {
    padding: 1.25rem 1.25rem 0;
  }
  .vs-dp-stage {
    --vs-dp-cell-min: 54px;
  }
}

@media (min-width: 1081px) {
  .vs-viz-inner {
    grid-template-columns: minmax(0, 1fr) 340px;
    gap: 1.75rem;
  }
  .vs-info-panel {
    position: sticky;
    top: 80px;
  }
  .vs-complexity-grid {
    grid-template-columns: repeat(2, minmax(0, 1fr));
  }
}

@media (min-width: 901px) and (max-width: 1080px) {
  .vs-complexity-grid {
    grid-template-columns: repeat(4, minmax(0, 1fr));
  }
}