:root {
  --bg: #0f1114;
  --panel: #161a1f;
  --cell: #1d2126;
  --stroke: #2a2f36;
  --text: #e8eaed;
  --muted: #a0a7b4;
  --accent: #d6b46a;
  --ok: #7dd3fc;
  --warn: #fca5a5;
  --radius: 12px;
  --shadow: 0 10px 30px rgba(0, 0, 0, 0.25);
  --transition-duration: 160ms;
  color-scheme: dark;
  font-family: "Inter", "Segoe UI", system-ui, sans-serif;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  background: radial-gradient(circle at top, rgba(214, 180, 106, 0.08), transparent 40%), var(--bg);
  color: var(--text);
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 32px;
  padding: 32px clamp(20px, 5vw, 56px);
}

.playground {
  width: 100%;
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(280px, 1fr));
  gap: 24px;
  max-width: 960px;
}

.panel {
  background: linear-gradient(160deg, rgba(29, 33, 38, 0.92), rgba(19, 22, 27, 0.92));
  border: 1px solid var(--stroke);
  border-radius: var(--radius);
  padding: 24px;
  box-shadow: var(--shadow);
  display: flex;
  flex-direction: column;
  gap: 16px;
}

.panel-header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
}

.panel-toggle {
  border: 1px solid rgba(214, 180, 106, 0.4);
  border-radius: 999px;
  padding: 4px 12px;
  font-size: 0.75rem;
  text-transform: uppercase;
  letter-spacing: 0.08em;
  color: var(--muted);
  background: transparent;
  cursor: pointer;
  transition: color var(--transition-duration) ease, border-color var(--transition-duration) ease,
    background var(--transition-duration) ease;
}

.panel-toggle:hover,
.panel-toggle:focus-visible {
  color: var(--accent);
  border-color: var(--accent);
  background: rgba(214, 180, 106, 0.12);
  outline: none;
}

.panel[data-collapsed="true"] .panel-body {
  display: none;
}

.panel[data-collapsed="true"] .panel-toggle {
  color: var(--accent);
  border-color: rgba(214, 180, 106, 0.55);
}

.panel-title {
  margin: 0;
  font-size: 1rem;
  font-weight: 600;
  text-transform: uppercase;
  letter-spacing: 0.12em;
  color: var(--muted);
}

.panel-body {
  flex: 1;
  background: var(--cell);
  border: 1px solid rgba(42, 47, 54, 0.6);
  border-radius: calc(var(--radius) - 4px);
  display: grid;
  place-items: center;
  min-height: 240px;
  position: relative;
  overflow: hidden;
}

.panel-body.array-view {
  min-height: auto;
  max-height: clamp(160px, 32vh, 280px);
  overflow-y: auto;
  align-content: start;
  justify-items: stretch;
  padding: clamp(10px, 2.5vw, 18px);
  gap: clamp(4px, 1.4vw, 10px);
}

.array-view {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(32px, 48px));
  justify-content: center;
}

.array-item {
  width: 100%;
  aspect-ratio: 1;
  border-radius: 8px;
  background: rgba(214, 180, 106, 0.1);
  border: 1px solid rgba(214, 180, 106, 0.35);
  display: grid;
  place-items: center;
  color: var(--text);
  font-weight: 600;
  font-variant-numeric: tabular-nums;
  transition: transform var(--transition-duration) ease, border-color var(--transition-duration) ease, background var(--transition-duration) ease;
  position: relative;
  overflow: hidden;
  cursor: pointer;
  font-size: clamp(0.7rem, 1.6vw, 0.9rem);
  padding: 2px;
}

.array-item--highlight {
  background: rgba(125, 211, 252, 0.25);
  border-color: rgba(125, 211, 252, 0.7);
  transform: translateY(-4px);
}

.array-item[data-step-kind]::after {
  content: attr(data-step-kind);
  position: absolute;
  inset: auto 4px 4px 4px;
  font-size: 0.55rem;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  text-align: right;
  color: var(--accent);
  opacity: 0.9;
}

.array-item[data-step-kind="compare"]::after {
  color: var(--ok);
}

.array-item[data-step-kind="remove"]::after {
  color: var(--warn);
}

.tree-view {
  padding: 0;
}

.tree-canvas {
  width: 100%;
  height: 100%;
}

.tree-node {
  transition: transform var(--transition-duration) ease;
  cursor: pointer;
}

.tree-node__circle {
  fill: rgba(214, 180, 106, 0.15);
  stroke: rgba(214, 180, 106, 0.6);
  stroke-width: 1.5;
  transition: fill var(--transition-duration) ease, stroke var(--transition-duration) ease;
}

.tree-node__label {
  fill: var(--text);
  font-size: 16px;
  font-weight: 600;
  font-variant-numeric: tabular-nums;
}

.tree-node--highlight .tree-node__circle {
  fill: rgba(125, 211, 252, 0.25);
  stroke: rgba(125, 211, 252, 0.8);
}

.tree-node[data-step-kind="remove"] .tree-node__circle {
  stroke: rgba(252, 165, 165, 0.8);
  fill: rgba(252, 165, 165, 0.25);
}

.tree-node[data-step-kind="compare"] .tree-node__circle {
  stroke-dasharray: 6 4;
  stroke: rgba(125, 211, 252, 0.8);
}

.tree-edge {
  stroke: rgba(125, 211, 252, 0.25);
  stroke-width: 2;
  transition: stroke var(--transition-duration) ease, stroke-width var(--transition-duration) ease;
}

.tree-edge[data-step-kind="swap"] {
  stroke: rgba(214, 180, 106, 0.75);
  stroke-width: 3;
}

@media (max-width: 600px) {
  .panel-body.array-view {
    max-height: 220px;
    padding: 12px;
    gap: 6px;
  }

  .array-view {
    grid-template-columns: repeat(auto-fit, minmax(28px, 40px));
  }

  .array-item {
    min-height: 36px;
  }

  .panel {
    padding: 20px;
  }

  .panel-toggle {
    font-size: 0.7rem;
    padding-inline: 10px;
  }
}

.game-title {
  margin: 0;
  font-size: clamp(1.8rem, 4vw, 2.6rem);
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--muted);
}

.controls-panel {
  width: 100%;
  max-width: 780px;
  background: linear-gradient(175deg, rgba(23, 27, 32, 0.95), rgba(15, 17, 22, 0.95));
  border: 1px solid var(--stroke);
  border-radius: var(--radius);
  box-shadow: var(--shadow);
  padding: clamp(18px, 3.6vw, 26px);
  display: grid;
  gap: 12px;
}

.controls {
  display: grid;
  gap: 10px;
  justify-items: center;
}

.control-row {
  display: grid;
  gap: 8px;
  width: min(100%, 640px);
}

.control-row--value {
  grid-template-columns: minmax(0, 1fr) minmax(0, 1fr) auto;
  gap: 10px;
  align-items: center;
  width: 100%;
}

.control-row--buttons {
  display: flex;
  flex-wrap: wrap;
  gap: 8px;
  justify-content: center;
  margin: 0 auto;
}

.control-row--split {
  display: grid;
  grid-template-columns: repeat(auto-fit, minmax(160px, 1fr));
  gap: 10px;
}

.control-row--slider {
  display: grid;
  grid-template-columns: max-content 1fr max-content;
  gap: 12px;
  align-items: center;
}

.control-row--toggle {
  display: flex;
  align-items: center;
}

.control-label {
  font-size: 0.85rem;
  text-transform: uppercase;
  letter-spacing: 0.14em;
  color: var(--muted);
}

.control-input {
  background: rgba(29, 33, 38, 0.85);
  border: 1px solid rgba(42, 47, 54, 0.9);
  border-radius: calc(var(--radius) - 6px);
  padding: 10px 14px;
  color: var(--text);
  font-size: 1rem;
  transition: border-color var(--transition-duration) ease, box-shadow var(--transition-duration) ease;
}

.control-input:focus {
  outline: none;
  border-color: rgba(125, 211, 252, 0.7);
  box-shadow: 0 0 0 2px rgba(125, 211, 252, 0.2);
}

.control-range {
  width: 100%;
  accent-color: var(--accent);
}

.control-toggle {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  font-size: 0.95rem;
  color: var(--text);
}

.control-help {
  font-size: 0.8rem;
  color: var(--muted);
}

.control-subgroup {
  display: grid;
  gap: 6px;
}

.button {
  display: inline-flex;
  align-items: center;
  justify-content: center;
  padding: 8px 14px;
  border-radius: calc(var(--radius) - 6px);
  border: 1px solid rgba(42, 47, 54, 0.9);
  background: linear-gradient(180deg, rgba(29, 33, 38, 0.9), rgba(21, 24, 29, 0.9));
  color: var(--text);
  font-weight: 600;
  letter-spacing: 0.04em;
  cursor: pointer;
  transition: transform var(--transition-duration) ease, border-color var(--transition-duration) ease, background var(--transition-duration) ease;
}

.button:hover,
.button:focus-visible {
  transform: translateY(-2px);
  border-color: rgba(214, 180, 106, 0.7);
}

.button:disabled {
  opacity: 0.5;
  cursor: not-allowed;
}

.button--ghost {
  background: transparent;
  border: 1px solid rgba(214, 180, 106, 0.35);
  color: var(--accent);
}

.control-feedback {
  min-height: 1.2rem;
  font-size: 0.85rem;
  color: var(--muted);
}

.control-feedback[data-tone="success"] {
  color: var(--ok);
}

.control-feedback[data-tone="error"] {
  color: var(--warn);
}

.live-status {
  border-radius: var(--radius);
  border: 1px solid rgba(125, 211, 252, 0.25);
  padding: 16px 20px;
  max-width: min(720px, 100%);
  background: rgba(125, 211, 252, 0.06);
  color: var(--ok);
  font-size: 0.95rem;
  transition: border-color var(--transition-duration) ease, background var(--transition-duration) ease;
}

@media (max-width: 768px) {
  body {
    padding: 24px clamp(16px, 6vw, 28px);
    gap: 24px;
  }

  .panel-body {
    min-height: 200px;
  }

  .control-row--value {
    grid-template-columns: 1fr;
  }

  .control-row--slider {
    grid-template-columns: 1fr;
  }

  .control-row--buttons {
    justify-content: stretch;
  }

  .controls-panel {
    gap: 12px;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.01ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.01ms !important;
    scroll-behavior: auto !important;
  }
}