style.css

body {
    background-color: white;
    font-family: Arial, sans-serif;
}

.game-container {
    display: flex;
    flex-direction: column;
    align-items: center;
    justify-content: center;
    height: 100vh;
}

.sudoku-grid {
    display: grid;
    grid-template-columns: repeat(9, 1fr);
    gap: 2px;
}

.cell {
    width: 40px;
    height: 40px;
    display: flex;
    justify-content: center;
    align-items: center;
    border: 1px solid black;
    font-size: 24px;
    cursor: pointer;
}

.cell.filled {
    background-color: lightgray;
}

.cell.selected {
    background-color: yellow;
}

.cell.error {
    background-color: red;
}

.bold-border {
    border-width: 3px;
}

.restart-button {
    margin-top: 20px;
    padding: 10px 20px;
    font-size: 18px;
    cursor: pointer;
}

.popup {
    position: fixed;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    background-color: white;
    padding: 20px;
    border: 1px solid black;
    display: none;
}

.popup button {
    margin-top: 20px;
    padding: 10px 20px;
    font-size: 18px;
    cursor: pointer;
}