body {
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
    margin: 0;
    background-color: #f0f0f0;
}

.board {
    display: grid;
    grid-template-columns: repeat(4, 100px);
    grid-template-rows: repeat(4, 100px);
    gap: 5px;
}
.board1 {
    display: grid;
    grid-template-columns: repeat(4, 100px);
    grid-template-rows: repeat(5, 100px);
    gap: 5px;
}
.board2 {
    display: grid;
    grid-template-columns: repeat(4, 100px);
    grid-template-rows: repeat(6, 100px);
    gap: 5px;
}
.board3 {
    display: grid;
    grid-template-columns: repeat(4, 100px);
    grid-template-rows: repeat(7, 100px);
    gap: 5px;
}

.card {
    width: 100px;
    height: 100px;
    background-color: #ccc;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 2em;
    cursor: pointer;
    border-radius: 5px;
}

.card.open {
    background-color: #fff;
}

.card.match {
    background-color: #90ee90;
    cursor: default;
}
.timer {
    background-color: cadetblue;
    text-align: center;
}
button {
    background-color: #90ee90;
    margin: auto;
    display: block;
    margin-top: 20px;
}
h1 {
    text-align: center;
    color: brown;
}