:root {
  --bg: #0d1117;
  --card: #161b22;
  --accent: #38bdf8;
  --accent-soft: #79c9f8;
  --text: #e5e7eb;
  --text-muted: #94a3b8;
  --border: rgba(148, 163, 184, 0.16);
  --success: #22c55e;
  --danger: #fb7185;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  font-family: Inter, system-ui, -apple-system, BlinkMacSystemFont, "Segoe UI", sans-serif;
  color: var(--text);
  background: radial-gradient(circle at top, #111827 0%, #090b10 60%);
}

.app-shell {
  max-width: 560px;
  margin: 0 auto;
  padding: 24px 18px 36px;
}

header {
  text-align: center;
  margin-bottom: 24px;
}

h1 {
  margin: 0;
  font-size: clamp(2rem, 4vw, 2.6rem);
}

p {
  margin: 8px 0 0;
  color: var(--text-muted);
}

.status-bar {
  display: grid;
  grid-template-columns: repeat(3, minmax(0, 1fr));
  gap: 12px;
  margin-bottom: 20px;
}

.status-item {
  background: rgba(255, 255, 255, 0.04);
  border: 1px solid var(--border);
  border-radius: 16px;
  padding: 16px;
  text-align: center;
}

.status-item span {
  display: block;
  font-size: 0.9rem;
  color: var(--text-muted);
}

.status-item strong {
  font-size: 1.4rem;
}

.board-shell {
  background: rgba(255, 255, 255, 0.03);
  border: 1px solid var(--border);
  border-radius: 24px;
  padding: 16px;
}

.board {
  display: grid;
  grid-template-columns: repeat(4, 1fr);
  gap: 12px;
}

.tile {
  aspect-ratio: 1 / 1;
  border-radius: 18px;
  display: grid;
  place-items: center;
  font-size: 1.6rem;
  font-weight: 700;
  user-select: none;
  cursor: pointer;
  transition: transform 0.15s ease, background-color 0.15s ease, opacity 0.15s ease;
  background: #161b22;
  border: 1px solid var(--border);
  color: var(--text);
}

.tile:hover {
  transform: translateY(-2px);
}

.tile.selected {
  background: linear-gradient(135deg, #38bdf8 0%, #0ea5e9 100%);
  border-color: rgba(56, 189, 248, 0.55);
  color: #fff;
}

.tile.removing {
  opacity: 0.15;
  transform: scale(0.96);
}

.controls {
  margin-top: 20px;
  display: flex;
  flex-direction: column;
  gap: 12px;
  align-items: center;
}

button {
  border: none;
  border-radius: 999px;
  background: linear-gradient(135deg, #38bdf8 0%, #0ea5e9 100%);
  color: #0f172a;
  padding: 14px 22px;
  font-size: 1rem;
  cursor: pointer;
  box-shadow: 0 18px 40px rgba(14, 165, 233, 0.18);
}

button:hover {
  transform: translateY(-1px);
}

.hint {
  color: var(--text-muted);
  text-align: center;
  font-size: 0.95rem;
  max-width: 420px;
}

.overlay {
  position: fixed;
  inset: 0;
  background: rgba(0, 0, 0, 0.72);
  display: grid;
  place-items: center;
  z-index: 20;
}

.overlay.hidden {
  display: none;
}

.overlay-panel {
  background: #0f172a;
  border: 1px solid rgba(148, 163, 184, 0.18);
  border-radius: 24px;
  padding: 28px 30px;
  text-align: center;
  width: min(420px, calc(100% - 40px));
}

.overlay-panel h2 {
  margin: 0 0 12px;
  font-size: 1.8rem;
}

.overlay-panel p {
  margin: 0 0 22px;
  color: var(--text-muted);
}

.overlay-panel span {
  color: var(--accent-soft);
  font-weight: 700;
}

@media (max-width: 520px) {
  .board {
    gap: 10px;
  }
  .status-bar {
    grid-template-columns: 1fr;
  }
}