ul {
    list-style-type: none;
    padding-left: 20px; /* 调整子文件夹的缩进 */
}
.folder {
    cursor: pointer;
    padding-left: 20px; /* 调整图标和文字之间的间距 */
    position: relative;
    font-weight: thin;
}
.folder > span {
    padding-left: 25px; /* 调整图标和文字之间的间距 */
    position: relative;
}
.folder > span::before {
    content: '';
    display: inline-block;
    width: 20px;
    height: 20px;
    background-image: url('icon/folder.png');
    background-size: 20px 20px;
    position: absolute;
    left: 0;
    top: 50%;
    transform: translateY(-50%);
}

.file {
    cursor: pointer;
    padding: 5px;
}

.folder.expanded > span {
    font-size: 1.5em;
}