body {
    font-family: Arial, sans-serif;
    text-align: center;
}
#timer {
    
}
#game-board {
    display: grid;
    grid-template-columns: repeat(4, 100px);
    grid-template-rows: repeat(4, 100px);
    grid-gap: 10px;
    justify-content: center;
    margin: 30px auto;
}
.card {
    background-color: #ccc;
    border-radius: 5px;
    cursor: pointer;
}
.card .card-content {
    opacity: 0;
  }
.card.flip .card-content{
    opacity: 1;
}
.card.matched {
  border: solid 4px rgb(0, 255, 0);
  box-sizing: border-box; 
  cursor: default;
}
.card .card-content {
    max-width: 100%;
}

.no-click {
    pointer-events: none;
}