.layui-treetable i.folder-close{
    background: url(folder-closed.gif) 0 0 no-repeat;
    padding: 0 0 0 16px;
}

.layui-treetable i.folder{
    background: url(folder.gif) 0 0 no-repeat;
    padding: 0 0 0 16px;
}

.layui-treetable i.leaf{
    background: url(file.gif) 0 0 no-repeat;
    padding: 0 0 0 16px;
}