body {
    background-color: #121212;
    color: #ffffff;
    font-family: Arial, sans-serif;
    margin: 0;
    padding: 0;
    display: flex;
    justify-content: center;
    align-items: center;
    height: 100vh;
}

.container {
    text-align: center;
    width: 90%;
    max-width: 600px;
}

h1 {
    margin-bottom: 20px;
}

.controls {
    margin-bottom: 20px;
}

.board {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    gap: 2px;
    background-color: #333;
    padding: 10px;
    border: 2px solid #444;
    border-radius: 5px;
}

.cell {
    width: 40px;
    height: 40px;
    display: flex;
    justify-content: center;
    align-items: center;
    background-color: #1e1e1e;
    color: #fff;
    font-size: 18px;
    border: 1px solid #444;
    cursor: pointer;
}

.cell:focus {
    outline: 2px solid #007bff;
}

.cell.error {
    background-color: #ff4c4c;
}

#message {
    margin-top: 20px;
    font-size: 16px;
}