#puzzle-container {
    display: grid;
    grid-template-columns: repeat(4, 100px);
    grid-template-rows: repeat(4, 100px);
    gap: 5px;
    width: 420px; /* 4*100px + 3*5px */
    height: 420px; /* 4*100px + 3*5px */
    border: 2px solid #333;
    margin: 20px auto;
    position: relative;
}

.puzzle-tile {
    width: 100px;
    height: 100px;
    background-color: #f0f0f0;
    border: 1px solid #ccc;
    display: flex;
    justify-content: center;
    align-items: center;
    color: #333;
    font-size: 2em;
    font-weight: bold;
    cursor: pointer;
    transition: all 0.2s ease-in-out;
    
    box-sizing: border-box; /* Include padding and border in the element's total width and height */
}

.puzzle-tile[data-value="1"] { background-color: #ff9999; }
.puzzle-tile[data-value="2"] { background-color: #99ff99; }
.puzzle-tile[data-value="3"] { background-color: #9999ff; }
.puzzle-tile[data-value="4"] { background-color: #ffff99; }
.puzzle-tile[data-value="5"] { background-color: #ff99ff; }
.puzzle-tile[data-value="6"] { background-color: #99ffff; }
.puzzle-tile[data-value="7"] { background-color: #ffcc99; }
.puzzle-tile[data-value="8"] { background-color: #cc99ff; }
.puzzle-tile[data-value="9"] { background-color: #99ccff; }
.puzzle-tile[data-value="10"] { background-color: #ffccff; }
.puzzle-tile[data-value="11"] { background-color: #ccff99; }
.puzzle-tile[data-value="12"] { background-color: #cc99cc; }
.puzzle-tile[data-value="13"] { background-color: #ff9999; }
.puzzle-tile[data-value="14"] { background-color: #99ffcc; }
.puzzle-tile[data-value="15"] { background-color: #ccffcc; }

.puzzle-tile.empty {
    background-color: #e0e0e0;
    cursor: default;
}

.puzzle-tile:not(.empty):hover {
    background-color: #ddd;
}

#shuffle-button {
    display: block;
    margin: 20px auto;
    padding: 10px 20px;
    font-size: 1.2em;
    cursor: pointer;
}

#message {
    text-align: center;
    font-size: 1.2em;
    background-color: #333;
    color: #fff;
    padding: 10px;
    border-radius: 5px;
    margin-top: 20px;
}

.win-message {
    color: green;
    font-weight: bold;
}