body {
  font-family: Arial, sans-serif;
  text-align: center;
  background: linear-gradient(135deg, #89f7fe, #66a6ff);
  margin: 0;
  padding: 20px;
}

.game-board {
  display: grid;
  grid-template-columns: repeat(4, 100px);
  grid-gap: 15px;
  justify-content: center;
  margin: 30px auto;
}

.card {
  width: 100px;
  height: 100px;
  background: #444;
  border-radius: 10px;
  cursor: pointer;
  font-size: 2rem;
  display: flex;
  align-items: center;
  justify-content: center;
  color: transparent;
  transition: transform 0.3s;
}

.card.flipped {
  background: #fff;
  color: #333;
  transform: rotateY(180deg);
}