body {
  font-family: sans-serif;
  text-align: center;
  background-color: #f4f4f4;
}

#game-board {
  display: grid;
  grid-template-columns: repeat(4, 80px);
  grid-gap: 10px;
  justify-content: center;
  margin-top: 20px;
}

.card {
  width: 80px;
  height: 80px;
  background-color: #888;
  color: white;
  display: flex;
  justify-content: center;
  align-items: center;
  font-size: 2em;
  cursor: pointer;
  border-radius: 8px;
}

.card.revealed {
  background-color: #4CAF50;
}