body {
    margin: 0;
    padding: 0;
    display: flex;
    align-items: center;
    justify-content: center;
    min-height: 100vh;
    background-color: #f0f4f8;
    font-family: 'Arial', sans-serif;
    flex-direction: column;
    box-sizing: border-box;
}

.board {
    display: grid;
    grid-template-columns: repeat(3, 1fr);
    grid-template-rows: repeat(3, 1fr);
    gap: 8px;
    max-width: 350px;
    max-height: 350px;
    width: 100%;
    height: 100vh;
    background-color: #fff;
    padding: 10px;
    border-radius: 15px;
    box-shadow: 0 4px 12px rgba(0, 0, 0, 0.1);
}

.cell {
    width: 100%;
    height: 100%;
    display: flex;
    align-items: center;
    justify-content: center;
    font-size: 36px;
    font-weight: bold;
    color: #333;
    background-color: #f9f9f9;
    border: 1px solid #ddd;
    border-radius: 8px;
    cursor: pointer;
    transition: background-color 0.3s, transform 0.3s ease, box-shadow 0.3s ease;
}

.cell:hover {
    background-color: #e0e0e0;
    transform: scale(1.1);
    box-shadow: 0 0 8px rgba(0, 0, 0, 0.2);
}

#game-board {
    background-color: #f4f4f9;
    padding: 20px;
    border-radius: 15px;
    box-shadow: 0 8px 20px rgba(0, 0, 0, 0.15);
    margin-bottom: 20px;
}

#game-over-message {
    font-size: 20px;
    font-weight: bold;
    color: #333;
    margin-top: 15px;
    text-align: center;
    display: none;
}

#restart-button {
    margin-top: 20px;
    padding: 12px 18px;
    font-size: 18px;
    font-weight: 600;
    cursor: pointer;
    background-color: #4caf50;
    color: #fff;
    border: none;
    border-radius: 8px;
    transition: background-color 0.3s, transform 0.3s ease;
}

#restart-button:hover {
    background-color: #45a049;
    transform: scale(1.05);
}

@media screen and (max-width: 600px) {
    .board {
        max-width: 90%;
        grid-template-columns: repeat(3, 1fr);
        grid-template-rows: repeat(3, 1fr);
    }

    #game-board {
        padding: 15px;
    }

    #game-over-message {
        font-size: 18px;
    }

    #restart-button {
        font-size: 16px;
        padding: 10px 15px;
    }
}