style.css

#left-panel {
    height: 90%;
    overflow-y: auto;
    border-right: 1px solid #ccc;
}

#right-panel {
    height: 90%;
    overflow-y: auto;
}

#combine-button {
    position: absolute;
    bottom: 10px;
    left: 10px;
    width: calc(100% - 20px);
    background-color: orange;
    color: white;
}

#download-zip {
    position: absolute;
    bottom: 10px;
    right: 10px;
    width: calc(100% - 20px);
    background-color: blue;
    color: white;
}