body {
    font-family: Arial, sans-serif;
    background-color: #f7f7f7;
    height: 100vh;
}

h1 {
    margin-top: 0;
}

#game-board {
    display: grid;
    grid-template-columns: repeat(6, 1fr);
    grid-template-rows: repeat(6, 1fr);
    grid-gap: 10px;
    width: 600px;
    height: 600px;
    margin-bottom: 20px;
}

.card {
    position: relative;
    perspective: 1000px;
}

.card .front,
.card .back {
    position: absolute;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 50px;
    width: 100%;
    height: 100%;
    backface-visibility: hidden;
    border-radius: 5px;
}

.card .front {
    background-color: #ffffff;
    color: #000000;
}

.card .back {
    background-color: #000000;
    color: #ffffff;
    transform: rotateY(180deg);
}
.card .back .back-text {
    font-size: 1.5rem !important;
}
.card.flip .front {
    transform: rotateY(180deg);
}

.card.flip .back {
    transform: rotateY(0deg);
}
.card.flip .back.second {
    font-size: 1.2em;
}
.score {
    display: block;
    margin-top: 20px;
    margin-bottom: 20px;
    font-size: 24px;
}
.flash {
    background-color: green;
    color: #fff;
    position: fixed;
    top: 0;
    left: 0;
    right: 0;
    text-align: center;
    padding: 10px;
    display: none;
}