:root {
  color-scheme: dark;
  font-family: "Inter", "Fira Sans", system-ui, -apple-system, sans-serif;
  --bg: #0f1114;
  --panel: #161a1f;
  --cell: #1d2126;
  --stroke: #2a2f36;
  --text: #e8eaed;
  --muted: #c7cedd;
  --accent: #d6b46a;
  --ok: #7dd3fc;
  --warn: #fca5a5;
  --radius: 16px;
  --transition: 160ms ease;
}

* {
  box-sizing: border-box;
}

body {
  line-height: 1.55;
  margin: 0;
  min-height: 100vh;
  background: radial-gradient(circle at top, rgba(214, 180, 106, 0.06), transparent 42%), var(--bg);
  color: var(--text);
  display: flex;
  justify-content: center;
  align-items: flex-start;
  padding: clamp(0.5rem, 4vw, 1.5rem);
  overflow-x: hidden;
}

#app {
  width: min(94vw, 420px);
  background: var(--panel);
  border-radius: var(--radius);
  border: 1px solid var(--stroke);
  box-shadow: 0 22px 48px rgba(3, 6, 11, 0.4);
  display: flex;
  flex-direction: column;
  gap: clamp(0.9rem, 3vw, 1.6rem);
  padding: clamp(1rem, 4vw, 2rem);
  box-sizing: border-box;
  margin: 0 auto;
}

.board-shell {
  width: 100%;
  display: flex;
  justify-content: center;
  border-radius: calc(var(--radius) - 6px);
  background: linear-gradient(145deg, rgba(29, 33, 38, 0.65), rgba(22, 26, 31, 0.5));
  border: 1px solid var(--stroke);
  transition: background var(--transition);
  padding: clamp(0.45rem, 3vw, 0.9rem);
  box-sizing: border-box;
}

.app-header {
  display: grid;
  gap: clamp(0.75rem, 3vw, 1.4rem);
  width: 100%;
  text-align: center;
}

.app-header h1 {
  margin: 0;
  font-size: clamp(1.75rem, 4vw, 2.2rem);
}

.control-toolbar {
  display: flex;
  flex-wrap: wrap;
  align-items: center;
  justify-content: center;
  gap: clamp(0.35rem, 2.5vw, 0.9rem);
}

.control {
  display: grid;
  gap: 0.35rem;
  color: var(--muted);
  font-size: 0.95rem;
}

.control select {
  background: var(--cell);
  color: var(--text);
  border: 1px solid var(--stroke);
  border-radius: calc(var(--radius) / 2);
  padding: 0.5rem 1rem;
  font: inherit;
  cursor: pointer;
  transition: border-color var(--transition), background var(--transition);
}

.control select:focus-visible {
  outline: 2px solid var(--accent);
  outline-offset: 2px;
}

.control-buttons {
  display: flex;
  flex-wrap: wrap;
  justify-content: center;
  gap: 0.5rem;
}

button,
select {
  min-height: 44px;
}

button {
  appearance: none;
  border: 1px solid transparent;
  border-radius: calc(var(--radius) / 2);
  padding: 0.6rem 1.3rem;
  font: inherit;
  cursor: pointer;
  background: var(--cell);
  color: var(--text);
  transition: transform var(--transition), border-color var(--transition), background var(--transition);
  outline: none;
}

button.primary {
  border-color: rgba(214, 180, 106, 0.6);
  box-shadow: 0 8px 22px rgba(214, 180, 106, 0.18);
}

button:hover,
button:focus-visible {
  transform: translateY(-1px);
  background: rgba(125, 211, 252, 0.12);
  border-color: var(--ok);
}

button:active {
  transform: translateY(0);
}

.moves {
  color: var(--muted);
  font-variant-numeric: tabular-nums;
}

@media (max-width: 640px) {
  body {
    align-items: flex-start;
    padding: clamp(0.4rem, 6vw, 1rem);
  }

  #app {
    width: min(96vw, 360px);
    padding: clamp(0.75rem, 6vw, 1.4rem);
    gap: clamp(0.7rem, 4vw, 1.2rem);
  }

  .control-toolbar {
    gap: clamp(0.3rem, 4vw, 0.7rem);
  }

  .control,
  .control-buttons button {
    width: 100%;
  }
}

@media (min-width: 960px) {
  #app {
    width: min(420px, 38vw);
  }

  .board-shell {
    padding: 0.75rem;
  }
}

.sr-only {
  position: absolute;
  width: 1px;
  height: 1px;
  padding: 0;
  margin: -1px;
  overflow: hidden;
  clip: rect(0, 0, 0, 0);
  white-space: nowrap;
  border: 0;
}

.board-shell[data-solved="true"] {
  box-shadow: 0 0 0 2px rgba(125, 211, 252, 0.35), 0 22px 48px rgba(3, 6, 11, 0.5);
}

#app[data-resizing="true"] .board-grid button {
  transition: none !important;
}

.board-grid {
  --board-size: 5;
  display: grid;
  grid-template-columns: repeat(var(--board-size), minmax(0, 1fr));
  gap: clamp(0.3rem, 2vw, 0.55rem);
  width: min(100%, clamp(220px, 90vw, 360px));
  margin: 0 auto;
  padding: clamp(0.4rem, 2vw, 0.9rem);
  box-sizing: border-box;
  justify-items: center;
}

.board-grid button {
  width: 100%;
  aspect-ratio: 1 / 1;
  border-radius: 14px;
  background: var(--cell);
  border: 1px solid var(--stroke);
  color: var(--muted);
  transition: background var(--transition), border-color var(--transition), transform var(--transition);
  box-shadow: inset 0 2px 6px rgba(10, 12, 15, 0.6);
}

.board-grid button:focus-visible {
  border-color: var(--accent);
  box-shadow: 0 0 0 3px rgba(214, 180, 106, 0.2);
}

.board-grid button.cell--hint {
  border-color: rgba(125, 211, 252, 0.85);
  box-shadow: 0 0 0 3px rgba(125, 211, 252, 0.35);
  transform: translateY(-4px);
}

.board-grid button.cell--preview {
  border-color: rgba(214, 180, 106, 0.5);
  box-shadow: 0 6px 18px rgba(214, 180, 106, 0.18);
  transform: translateY(-3px);
}

.board-grid button:hover {
  transform: translateY(-2px);
  border-color: var(--ok);
}

.board-grid button[data-active="true"],
.board-grid button.cell--active {
  background: linear-gradient(160deg, rgba(214, 180, 106, 0.28), rgba(214, 180, 106, 0.05));
  color: var(--text);
  border-color: rgba(214, 180, 106, 0.7);
}

.board-grid button.cell--solution {
  box-shadow: 0 0 0 2px rgba(125, 211, 252, 0.45);
  border-color: rgba(125, 211, 252, 0.6);
}

.board-grid button.cell--solution::after {
  content: attr(data-solution-order);
  position: absolute;
  top: 6px;
  right: 8px;
  width: 1.3rem;
  height: 1.3rem;
  border-radius: 50%;
  background: rgba(125, 211, 252, 0.28);
  color: var(--ok);
  font-size: 0.65rem;
  display: inline-flex;
  align-items: center;
  justify-content: center;
  font-variant-numeric: tabular-nums;
  opacity: var(--solution-opacity, 1);
}

.board-grid button.cell--solution[data-solution-depth="1"]::after {
  --solution-opacity: 1;
}

.board-grid button.cell--solution[data-solution-depth="2"]::after {
  --solution-opacity: 0.68;
}

.board-grid button.cell--solution[data-solution-depth="3"]::after {
  --solution-opacity: 0.4;
}

button[disabled],
button[aria-disabled='true'] {
  cursor: not-allowed;
  opacity: 0.6;
  transform: none;
}

main.board-shell:focus-visible {
  outline: 3px solid var(--ok);
  outline-offset: 4px;
}

@media (hover: none) {
  button:hover {
    transform: none;
  }
}

@media (prefers-reduced-motion: reduce) {
  *,
  *::before,
  *::after {
    animation-duration: 0.001ms !important;
    animation-iteration-count: 1 !important;
    transition-duration: 0.001ms !important;
  }
}

.app-footer {
  width: 100%;
  display: flex;
  justify-content: space-between;
  align-items: center;
  gap: 1rem;
  flex-wrap: wrap;
}

@keyframes tile-disco {
  0% {
    background: var(--cell);
    border-color: rgba(214, 180, 106, 0.4);
  }
  33% {
    background: rgba(33, 38, 48, 0.95);
    border-color: rgba(125, 211, 252, 0.8);
  }
  66% {
    background: rgba(45, 32, 48, 0.9);
    border-color: rgba(246, 173, 85, 0.75);
  }
  100% {
    background: var(--cell);
    border-color: rgba(214, 180, 106, 0.4);
  }
}

#app[data-solved="true"] .board-grid button {
  animation: tile-disco 2.6s ease-in-out infinite alternate;
}

#app[data-solved="true"] .board-grid button:nth-child(2n) {
  animation-delay: 0.5s;
}

#app[data-solved="true"] .board-grid button:nth-child(3n) {
  animation-delay: 1s;
}