:root {
  --bg: #0a101b;
  --panel: rgba(16, 25, 40, 0.7);
  --text: #eef2ff;
  --muted: rgba(238, 242, 255, 0.72);
  --border: rgba(238, 242, 255, 0.16);
  --accent: #2dd4bf;
  --accent-2: #fbbf24;
  --danger: #f87171;
  --cell: rgba(255,255,255,0.08);
  --shadow: 0 24px 60px rgba(3, 7, 18, 0.45);
  --font-display: "Trebuchet MS", "Gill Sans", "Segoe UI", sans-serif;
  --font-body: "Avenir Next", "Gill Sans", "Trebuchet MS", sans-serif;
}

[data-theme="light"] {
  --bg: #f7f4ee;
  --panel: rgba(255, 255, 255, 0.78);
  --text: #0f172a;
  --muted: rgba(15, 23, 42, 0.7);
  --border: rgba(15, 23, 42, 0.14);
  --accent: #0d9488;
  --accent-2: #d97706;
  --danger: #e11d48;
  --cell: rgba(15, 23, 42, 0.05);
  --shadow: 0 18px 40px rgba(15, 23, 42, 0.16);
}

* { box-sizing: border-box; }
body {
  margin: 0;
  font-family: var(--font-body);
  background:
    radial-gradient(900px 600px at 15% 10%, rgba(45, 212, 191, 0.18), transparent 60%),
    radial-gradient(700px 500px at 85% 15%, rgba(251, 191, 36, 0.14), transparent 60%),
    linear-gradient(160deg, rgba(15, 23, 42, 0.35), transparent 55%),
    var(--bg);
  color: var(--text);
  min-height: 100vh;
  position: relative;
}

body::before {
  content: '';
  position: fixed;
  inset: 0;
  background-image:
    linear-gradient(130deg, rgba(255, 255, 255, 0.04) 25%, transparent 25%),
    linear-gradient(230deg, rgba(255, 255, 255, 0.04) 25%, transparent 25%);
  background-size: 22px 22px;
  opacity: 0.25;
  pointer-events: none;
}

.container { max-width: 920px; margin: 0 auto; padding: 18px 14px 40px; position: relative; z-index: 1; animation: fadeUp 0.6s ease-out; }
.header { padding: 14px 14px 6px; display: grid; gap: 8px; }
.title { margin: 0; font-size: 32px; font-family: var(--font-display); letter-spacing: 0.4px; }
.subtitle { margin: 0; color: var(--muted); }

.controls {
  margin-top: 12px;
  padding: 14px;
  background: linear-gradient(140deg, rgba(255, 255, 255, 0.08), rgba(255, 255, 255, 0.02));
  border: 1px solid var(--border);
  border-radius: 14px;
  box-shadow: var(--shadow);
}

.button-row { display: flex; flex-wrap: wrap; gap: 10px; }
.btn {
  appearance: none;
  border: 1px solid var(--border);
  background: var(--cell);
  color: var(--text);
  padding: 10px 12px;
  border-radius: 12px;
  cursor: pointer;
  font-weight: 700;
  transition: transform 0.15s ease, box-shadow 0.2s ease, border-color 0.2s ease;
}
.btn.primary { border-color: rgba(45, 212, 191, 0.6); background: rgba(45, 212, 191, 0.18); box-shadow: 0 10px 20px rgba(45, 212, 191, 0.18); }
.btn.danger { border-color: rgba(248, 113, 113, 0.65); background: rgba(248, 113, 113, 0.12); }
.btn:hover { transform: translateY(-1px); }
.btn:focus-visible { outline: 2px solid var(--accent); outline-offset: 2px; }

.status { margin-top: 10px; color: var(--muted); font-size: 14px; display: flex; gap: 6px; flex-wrap: wrap; align-items: center; }
.status strong { color: var(--text); }

.game { margin-top: 14px; display: grid; place-items: center; }

.board {
  --size: 4;
  display: grid;
  grid-template-columns: repeat(var(--size), 1fr);
  width: min(92vw, 480px);
  aspect-ratio: 1 / 1;
  border: 2px solid var(--border);
  border-radius: 14px;
  overflow: hidden;
  background: rgba(0,0,0,0.12);
  box-shadow: var(--shadow);
  animation: fadeIn 0.5s ease-out;
}

.cell {
  position: relative;
  display: grid;
  place-items: center;
  background: var(--cell);
  border: 1px solid rgba(232,238,252,0.14);
  transition: background 0.2s ease, transform 0.2s ease;
}

[data-theme="light"] .cell { border-color: rgba(15,23,42,0.14); }
.cell:focus-within { background: rgba(45, 212, 191, 0.12); }

.cell .label {
  position: absolute;
  top: 6px;
  left: 6px;
  font-size: 11px;
  color: var(--muted);
  font-weight: 700;
  background: rgba(0, 0, 0, 0.18);
  padding: 2px 6px;
  border-radius: 999px;
}

.cell input {
  width: 100%;
  height: 100%;
  border: none;
  outline: none;
  background: transparent;
  text-align: center;
  font-size: clamp(16px, 4vw, 22px);
  font-weight: 800;
  font-family: var(--font-display);
  letter-spacing: 0.04em;
  color: var(--text);
  caret-color: var(--accent);
  transition: transform 0.15s ease;
}

.cell input.error { color: var(--danger); }
.cell input:focus-visible { transform: scale(1.04); }

/* thick cage borders */
.cell.btop { border-top-width: 3px; }
.cell.bleft { border-left-width: 3px; }
.cell.bright { border-right-width: 3px; }
.cell.bbottom { border-bottom-width: 3px; }

.theme-toggle {
  position: fixed;
  right: 14px;
  bottom: 14px;
  width: 46px;
  height: 46px;
  border-radius: 999px;
  border: 1px solid var(--border);
  background: var(--panel);
  color: var(--text);
  cursor: pointer;
  box-shadow: var(--shadow);
}

@media (max-width: 420px) {
  .btn { width: 100%; }
}

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(8px); }
  to { opacity: 1; transform: translateY(0); }
}

@keyframes fadeIn {
  from { opacity: 0; transform: scale(0.98); }
  to { opacity: 1; transform: scale(1); }
}

@media (prefers-reduced-motion: reduce) {
  .container, .board, .btn, .cell input { animation: none; transition: none; }
}