:root {
  --cols: 4;
  --rows: 5;
  --cell: 80px; /* JS で更新 */
  --bg: #0f172a; /* slate-900 */
  --panel: #111827; /* gray-900 */
  --grid: #1f2937; /* grid line */
  --accent: #60a5fa; /* blue-400 */
  --text: #e5e7eb; /* gray-200 */
  --muted: #9ca3af; /* gray-400 */
  --shadow: rgba(0,0,0,0.35);
}

* { box-sizing: border-box; }
html, body { height: 100%; }
body {
  margin: 0;
  font-family: system-ui, -apple-system, Segoe UI, Roboto, Noto Sans JP, Helvetica, Arial, "Apple Color Emoji", "Segoe UI Emoji";
  color: var(--text);
  background: radial-gradient(1200px 800px at 10% 10%, #0b1026, #0a0f22 50%, #070b18 100%);
}

.topbar {
  display: flex;
  justify-content: space-between;
  align-items: center;
  padding: 12px 16px;
}
.topbar h1 { margin: 0; font-size: 20px; letter-spacing: 0.04em; }
.controls { display: flex; gap: 8px; align-items: center; }
.controls button {
  background: #1f2937;
  color: var(--text);
  border: 1px solid #374151;
  padding: 6px 10px;
  border-radius: 8px;
  cursor: pointer;
}
.controls button:hover { border-color: #4b5563; }
.moves { color: var(--muted); }

.game-wrap {
  position: relative;
  display: grid;
  place-items: center;
  padding: 12px 16px 8px;
}

.board {
  position: relative;
  width: min(92vmin, 520px);
  aspect-ratio: 4 / 5;
  border-radius: 16px;
  box-shadow: 0 10px 20px var(--shadow), inset 0 0 0 1px #111827;
  background:
    repeating-linear-gradient(
      to right,
      transparent 0 calc(var(--cell) - 1px),
      var(--grid) calc(var(--cell) - 1px) var(--cell)
    ),
    repeating-linear-gradient(
      to bottom,
      transparent 0 calc(var(--cell) - 1px),
      var(--grid) calc(var(--cell) - 1px) var(--cell)
    ),
    linear-gradient(180deg, #0b1228, #0a1022);
  overflow: hidden;
}

.piece {
  position: absolute;
  display: grid;
  place-items: center;
  user-select: none;
  border-radius: 12px;
  border: 1px solid rgba(255,255,255,0.1);
  box-shadow: 0 6px 12px var(--shadow);
  transition: left 180ms cubic-bezier(.2,.7,.2,1), top 180ms cubic-bezier(.2,.7,.2,1);
  cursor: grab;
  will-change: left, top;
}
.piece.dragging { cursor: grabbing; transition: none !important; z-index: 10; }
.piece small { font-weight: 600; color: rgba(255,255,255,0.85); text-shadow: 0 1px 0 rgba(0,0,0,0.4); }

/* Color by type */
.piece.goal { background: linear-gradient(135deg, #f59e0b, #ef4444); }
.piece.vert { background: linear-gradient(135deg, #10b981, #059669); }
.piece.horiz { background: linear-gradient(135deg, #60a5fa, #3b82f6); }
.piece.small { background: linear-gradient(135deg, #a78bfa, #8b5cf6); }

/* Sizing via CSS variables computed from --cell */
.piece { width: calc(var(--cell)); height: calc(var(--cell)); }
.piece[data-w="2"] { width: calc(var(--cell) * 2); }
.piece[data-h="2"] { height: calc(var(--cell) * 2); }

/* Position */
.piece { left: 0; top: 0; }
.piece[data-x] { left: calc(var(--cell) * attr(data-x number)); }
.piece[data-y] { top: calc(var(--cell) * attr(data-y number)); }

/* Fallback for browsers without attr() in calc() for number (Safari older) via inline style set by JS */

/* Arrows */
.piece .arrow {
  position: absolute;
  width: 28px; height: 28px;
  background: rgba(15, 23, 42, 0.9);
  color: #e5e7eb;
  border: 1px solid #334155;
  border-radius: 8px;
  display: none;
  align-items: center;
  justify-content: center;
  font-size: 14px;
  cursor: pointer;
}
.piece.selected .arrow { display: flex; }
.piece .arrow:disabled { display: none; }
.arrow.up { top: -10px; left: 50%; transform: translateX(-50%); }
.arrow.down { bottom: -10px; left: 50%; transform: translateX(-50%); }
.arrow.left { left: -10px; top: 50%; transform: translateY(-50%); }
.arrow.right { right: -10px; top: 50%; transform: translateY(-50%); }

.overlay {
  position: absolute;
  inset: 0;
  display: grid;
  place-items: center;
  background: rgba(0,0,0,0.4);
}
.overlay.hidden { display: none; }
.overlay .dialog {
  background: #0b1228;
  border: 1px solid #1f2937;
  border-radius: 12px;
  padding: 18px 20px;
  min-width: 220px;
  text-align: center;
  box-shadow: 0 10px 20px var(--shadow);
}
.overlay .dialog h2 { margin: 0 0 8px; }
.overlay .dialog button {
  margin-top: 10px;
  background: #1f2937;
  color: var(--text);
  border: 1px solid #374151;
  padding: 8px 12px;
  border-radius: 8px;
  cursor: pointer;
}

.hint { color: var(--muted); text-align: center; padding: 8px 16px 16px; }