body {
    font-family: Arial, sans-serif;
    text-align: center;
    background: #f2f2f2;
}
#puzzle-container {
    width: 400px;
    height: 400px;
    display: grid;
    grid-template-columns: repeat(4, 1fr);
    grid-template-rows: repeat(4, 1fr);
    gap: 2px;
    background: #000;
}
.tile {
    background-image: url('puzzle.jpg');
    background-size: 400px 400px;
    cursor: pointer;
    box-shadow: 0 0 3px #333;
    display: flex;
    justify-content: center;
    align-items: center;
    font-weight: bold;
    font-size: 20px;
    color: white;
}
.empty {
    background: #ccc;
    cursor: default;
}