body {
    font-family: 'Arial', sans-serif;
    margin: 0;
    padding: 0;
    background-color: #f4f4f4;
    color: #333;
}

header,
footer {
    background-color: #4CAF50;
    color: #fff;
    padding: 1em;
    text-align: center;
}

.container {
    max-width: 800px;
    margin: 20px auto;
    padding: 20px;
    background-color: #fff;
    border-radius: 15px;
    box-shadow: 0 0 15px rgba(0, 0, 0, 0.1);
}

.level-selection {
    text-align: center;
    margin-bottom: 20px;
}

.level-selection label {
    font-size: 1.2em;
}

.level-selection select {
    padding: 8px;
    border-radius: 5px;
    border: 1px solid #ccc;
}

.score-panel {
    display: flex;
    justify-content: space-between;
    align-items: center;
    margin-top: 20px;
}

button {
    padding: 10px 20px;
    background-color: #4CAF50;
    color: #fff;
    border: none;
    border-radius: 5px;
    cursor: pointer;
}

.game-board {
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    gap: 10px;
    margin-bottom: 20px;
}

.card {
    height: 100px;
    background-color: #3498db;
    border-radius: 5px;
    display: flex;
    justify-content: center;
    align-items: center;
    font-size: 1.5em;
    cursor: pointer;
    perspective: 1000px;
    transition: transform 0.5s;
    transform-style: preserve-3d;
}

.card.flipped {
    transform: rotateY(180deg);
}

.front,
.back {
    position: absolute;
    width: 100%;
    height: 100%;
    display: flex;
    justify-content: center;
    align-items: center;
    backface-visibility: hidden;
}

.front {
    background-color: #ddd;
    border-radius: 5px;
}

.back {
    background-color: #3498db;
    border-radius: 5px;
    transform: rotateY(180deg);
}