body {
  font-family: Arial, sans-serif;
  background: #f0f4f8;
  display: flex;
  justify-content: center;
  align-items: center;
  min-height: 100vh;
  margin: 0;
}
.container {
  text-align: center;
}
.game-board {
  display: grid;
  grid-template-columns: repeat(4, 80px);
  grid-gap: 15px;
  justify-content: center;
  margin-top: 20px;
}
.card {
  width: 80px;
  height: 80px;
  background: #1e40af;
  color: white;
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 2rem;
  cursor: pointer;
  border-radius: 10px;
  user-select: none;
  transition: transform 0.3s;
}
.card.flip {
  background: #facc15;
  color: #1e40af;
  transform: rotateY(180deg);
}
button {
  padding: 8px 16px;
  font-size: 1rem;
  margin-top: 10px;
  cursor: pointer;
}