#drop-area {
    border: 2px dashed #ccc;
    padding: 20px;
    width: 300px;
    text-align: center;
    margin: 50px auto;
}
#drop-area.highlight {
    border-color: purple;
}
#progress-bar {
    width: 0%;
    height: 20px;
    background-color: green;
    margin-top: 10px;
}
.hidden {
    display: none;
}
#gallery img {
    width: 100px;
    margin: 10px;
}