:root {
  --board-bg: #bbada0;
  --cell-bg: #cdc1b4;
  --text-dark: #776e65;
  --text-light: #f9f6f2;
  --accent: #8f7a66;
  --gap: 12px;
  --radius: 6px;
  --grid-size: 4;
}

* {
  box-sizing: border-box;
}

body {
  margin: 0;
  min-height: 100vh;
  display: flex;
  align-items: center;
  justify-content: center;
  background: #faf8ef;
  font-family: "Helvetica Neue", Arial, sans-serif;
  color: var(--text-dark);
}

.container {
  width: 480px;
  max-width: 90vw;
}

.header {
  display: flex;
  align-items: center;
  justify-content: space-between;
  margin-bottom: 16px;
}

.title {
  font-size: 2.5rem;
  font-weight: bold;
  margin: 0;
  color: var(--text-dark);
}

.score-box {
  background: var(--board-bg);
  color: var(--text-light);
  border-radius: var(--radius);
  padding: 8px 20px;
  text-align: center;
  min-width: 80px;
}

.score-label {
  display: block;
  font-size: 0.75rem;
  text-transform: uppercase;
  opacity: 0.8;
}

.score-value {
  display: block;
  font-size: 1.5rem;
  font-weight: bold;
}

.controls {
  display: flex;
  justify-content: flex-end;
  margin-bottom: 16px;
}

.restart-btn {
  background: var(--accent);
  color: var(--text-light);
  border: none;
  border-radius: var(--radius);
  padding: 10px 18px;
  font-size: 0.95rem;
  font-weight: bold;
  cursor: pointer;
}

.restart-btn:hover {
  opacity: 0.9;
}

.board {
  position: relative;
  display: grid;
  grid-template-columns: repeat(var(--grid-size), 1fr);
  grid-template-rows: repeat(var(--grid-size), 1fr);
  gap: var(--gap);
  background: var(--board-bg);
  border-radius: var(--radius);
  padding: var(--gap);
  aspect-ratio: 1 / 1;
}

.grid-cell {
  background: var(--cell-bg);
  border-radius: var(--radius);
  aspect-ratio: 1 / 1;
}

.tiles {
  position: absolute;
  inset: 0;
  display: grid;
  grid-template-columns: repeat(var(--grid-size), 1fr);
  grid-template-rows: repeat(var(--grid-size), 1fr);
  gap: var(--gap);
  padding: var(--gap);
}

.tile {
  display: flex;
  align-items: center;
  justify-content: center;
  border-radius: var(--radius);
  font-size: 1.75rem;
  font-weight: bold;
  background: var(--tile-bg, var(--cell-bg));
  color: var(--tile-color, var(--text-dark));
}

.overlay {
  position: absolute;
  inset: 0;
  display: flex;
  align-items: center;
  justify-content: center;
  background: rgba(238, 228, 218, 0.73);
  border-radius: var(--radius);
}

.overlay[hidden] {
  display: none;
}

.overlay-content {
  text-align: center;
}

#overlay-message {
  font-size: 2rem;
  font-weight: bold;
  color: var(--text-dark);
  margin: 0 0 16px;
}

#overlay-btn {
  background: var(--accent);
  color: var(--text-light);
  border: none;
  border-radius: var(--radius);
  padding: 10px 20px;
  font-size: 1rem;
  font-weight: bold;
  cursor: pointer;
}

#overlay-btn:hover {
  opacity: 0.9;
}