* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;

  display: grid;
  place-items: center;

  background: #111827;

  font-family: Arial, sans-serif;

  --accent: #a855f7;
  --board: #374151;

  --off: #374151;
  --off-border: #4b5563;

  --on: #a855f7;
  --on-border: #c084fc;

  --glow: rgba(168, 85, 247, 0.7);

  --panel: #1f2937;
  --text: #ffffff;
  --text-muted: #9ca3af;

  --win: #4ade80;
}

.game {
  width: min(92vw, 400px);

  text-align: center;
}

h1 {
  margin: 0 0 18px;

  color: var(--text);

  font-size: 28px;
}

.home-btn {
  position: fixed;
  top: max(12px, env(safe-area-inset-top));
  left: 12px;

  z-index: 1000;

  display: inline-flex;
  align-items: center;
  gap: 6px;

  padding: 8px 11px;

  border: 1px solid rgba(255,255,255,.1);
  border-radius: 12px;

  background: rgba(15,18,32,.82);
  color: rgba(255,255,255,.8);

  text-decoration: none;

  font-family:
    -apple-system,
    BlinkMacSystemFont,
    "Segoe UI",
    Roboto,
    Helvetica,
    Arial,
    sans-serif;

  font-size: 10px;
  font-weight: 700;
  letter-spacing: .08em;

  backdrop-filter: blur(10px);
  -webkit-backdrop-filter: blur(10px);

  box-shadow: 0 4px 18px rgba(0,0,0,.2);

  transition:
    transform .15s ease,
    background .15s ease,
    color .15s ease;
}

.home-btn svg {
  width: 15px;
  height: 15px;

  fill: none;
  stroke: currentColor;

  stroke-width: 2;
  stroke-linecap: round;
  stroke-linejoin: round;
}

.home-btn:active {
  transform: scale(.93);
}

.home-btn:hover {
  background: rgba(255,255,255,.1);
  color: white;
}

/* --------------------------------
   Difficulty
-------------------------------- */

.difficulty {
  display: grid;

  grid-template-columns:
    repeat(3, 1fr);

  gap: 6px;

  margin-bottom: 10px;
}

.difficulty-button {
  border: 0;
  border-radius: 8px;

  padding: 9px 5px;

  background: #374151;
  color: #9ca3af;

  font-size: 14px;
  font-weight: bold;

  cursor: pointer;

  transition:
    background 0.15s ease,
    color 0.15s ease,
    transform 0.1s ease;
}

.difficulty-button.active {
  background: var(--accent);

  color: #ffffff;
}

.difficulty-button:active {
  transform: scale(0.96);
}


/* --------------------------------
   Themes
-------------------------------- */

.themes {
  display: none;

  grid-template-columns:
    repeat(4, 1fr);

  gap: 5px;

  margin-bottom: 10px;
}

.themes.visible {
  display: grid;
}

.theme-button {
  border: 0;
  border-radius: 7px;

  padding: 7px 3px;

  background: var(--panel);
  color: var(--text-muted);

  font-size: 12px;
  font-weight: bold;

  cursor: pointer;

  transition:
    background 0.15s ease,
    color 0.15s ease,
    transform 0.1s ease;
}

.theme-button.active {
  background: var(--accent);
  color: #ffffff;
}

.theme-button.locked {
  opacity: 0.55;
  cursor: default;
}

.theme-button:active:not(.locked) {
  transform: scale(0.96);
}


/* --------------------------------
   Stats
-------------------------------- */

.stats {
  display: flex;

  justify-content: center;

  gap: 18px;

  margin-bottom: 12px;

  color: var(--text-muted);

  font-size: 15px;
  font-weight: bold;
}


/* --------------------------------
   Board
-------------------------------- */

.board {
  width: 100%;
  aspect-ratio: 1;

  display: grid;

  grid-template-columns:
    repeat(3, 1fr);

  gap: 8px;

  padding: 8px;

  background: var(--board);

  border-radius: 14px;
}


/* --------------------------------
   Lights
-------------------------------- */

.light {
  border-radius: 10px;

  background: var(--off);
  border: 2px solid var(--off-border);

  cursor: pointer;

  transition:
    background 0.15s ease,
    transform 0.1s ease,
    box-shadow 0.15s ease;
}


/* ON */

.light.on {
  background: var(--on);

  border-color: var(--on-border);

  box-shadow:
    0 0 12px var(--glow);
}


/* Touch feedback */

.light:active {
  transform: scale(0.93);
}



/* --------------------------------
   Solve celebration
-------------------------------- */

.board.solved {
  animation: solvedPulse 0.7s ease-out;
}

@keyframes solvedPulse {

  0% {
    transform: scale(1);

    box-shadow:
      0 0 0 transparent;
  }

  30% {
    transform: scale(1.04);

    box-shadow:
      0 0 20px var(--glow),
      0 0 40px var(--glow);
  }

  60% {
    transform: scale(1.02);

    box-shadow:
      0 0 30px var(--glow),
      0 0 55px var(--glow);
  }

  100% {
    transform: scale(1);

    box-shadow:
      0 0 0 transparent;
  }
}


/* --------------------------------
   Win screen
-------------------------------- */

.win-message {
  display: none;

  margin-top: 14px;
  padding: 18px;

  text-align: center;

  background: var(--panel);

  border-radius: 14px;

  border: 1px solid var(--board);
}

.win-title {
  margin-bottom: 12px;

  color: var(--win);

  font-size: 25px;
  font-weight: bold;
}

.win-moves {
  color: var(--text-muted);

  font-size: 14px;
}

.win-moves strong {
  display: block;

  margin-top: 4px;

  color: var(--text);

  font-size: 22px;
}

.new-puzzle {
  margin-top: 16px;

  border: 0;
  border-radius: 9px;

  padding: 10px 18px;

  background: var(--accent);
  color: #ffffff;

  font-size: 15px;
  font-weight: bold;

  cursor: pointer;
}

.new-puzzle:active {
  transform: scale(0.95);
}


/* =================================
   THEMES
================================= */


/* Classic */

body[data-theme="classic"] {
  --accent: #a855f7;
  --board: #374151;

  --off: #374151;
  --off-border: #4b5563;

  --on: #a855f7;
  --on-border: #c084fc;

  --glow: rgba(168, 85, 247, 0.7);

  --panel: #1f2937;
  --text: #ffffff;
  --text-muted: #9ca3af;

  --win: #4ade80;
}


/* Forest */

body[data-theme="forest"] {
  --accent: #22c55e;
  --board: #24372b;

  --off: #17231b;
  --off-border: #35543e;

  --on: #16a34a;
  --on-border: #4ade80;

  --glow: rgba(34, 197, 94, 0.7);

  --panel: #1d3024;
  --text: #ffffff;
  --text-muted: #a7c9ae;

  --win: #bef264;
}


/* Sunset */

body[data-theme="sunset"] {
  --accent: #f97316;
  --board: #43251f;

  --off: #241512;
  --off-border: #61352c;

  --on: #f97316;
  --on-border: #fb923c;

  --glow: rgba(249, 115, 22, 0.7);

  --panel: #351d19;
  --text: #ffffff;
  --text-muted: #fdba74;

  --win: #facc15;
}


/* Ocean */

body[data-theme="ocean"] {
  --accent: #06b6d4;
  --board: #173443;

  --off: #10242e;
  --off-border: #285365;

  --on: #0891b2;
  --on-border: #22d3ee;

  --glow: rgba(6, 182, 212, 0.7);

  --panel: #12303c;
  --text: #ffffff;
  --text-muted: #a5d8e5;

  --win: #67e8f9;
}