body{
    background-color: gray;
}

.heading{
    text-align: center;
    font-size: 3rem;
    margin: 25px;
}

.cards_container {
  display: grid;
  grid-template-columns: repeat(4, 80px);
  grid-gap: 10px;
  justify-content: center;
  margin-top: 2rem;
}

.card {
  width: 80px;
  height: 80px;
  font-size: 2rem;
  text-align: center;
  line-height: 80px;
  background-color: #f2f2f2;
  border: 2px solid #ccc;
  cursor: pointer;
}

.card.matched {
  background-color: lightgreen;
  pointer-events: none;
}