body {
  margin: 0;
  font-family: sans-serif;
  text-align: center;
  background: #f0f0f0;
}

header, footer {
  padding: 10px;
  background: #333;
  color: white;
  display: flex;
  justify-content: center;
  gap: 20px;
  align-items: center;
}

main {
  margin: 20px 0;
  display: flex;
  justify-content: center;
  flex-direction: column;
  align-items: center;
}

#puzzleContainer, #completedImage {
  display: grid;
  border: 2px solid #333;
  margin-bottom: 10px;
}

.puzzle-piece {
  background-size: 100% 100%;
  cursor: pointer;
  box-sizing: border-box;
  border: 1px solid #ccc;
  user-select: none;
}

.puzzle-piece.blank {
  background: none;
  border: 1px solid transparent;
}

.puzzle-piece.blank {
  background-color: #88f; /* ← ここで色を指定 */
  border: 1px solid #999;
}