前端这种下拉可多选的框怎么实现的

下面是简体代码，可参考，好看的下拉框多选框架可以参考layui

<style>
/* 下拉多选样式 需要引用*/
select[multiple]+.layui-form-select>.layui-select-title>input.layui-input
    {
    border-bottom: 0
}

select[multiple]+.layui-form-select dd {
    padding: 0;
}

select[multiple]+.layui-form-select .layui-form-checkbox[lay-skin=primary]
    {
    margin: 0 !important;
    display: block;
    line-height: 36px !important;
    position: relative;
    padding-left: 26px;
}

select[multiple]+.layui-form-select .layui-form-checkbox[lay-skin=primary] span
    {
    line-height: 36px !important;
    padding-left: 10px;
    float: none;
}

select[multiple]+.layui-form-select .layui-form-checkbox[lay-skin=primary] i
    {
    position: absolute;
    left: 10px;
    top: 0;
    margin-top: 9px;
}

.multiSelect {
    line-height: normal;
    height: auto;
    padding: 4px 10px;
    overflow: hidden;
    min-height: 38px;
    margin-top: -38px;
    left: 0;
    z-index: 99;
    position: relative;
    background: none;
}

.multiSelect a {
    padding: 2px 5px;
    background: #908e8e;
    border-radius: 2px;
    color: #fff;
    display: block;
    line-height: 20px;
    height: 20px;
    margin: 2px 5px 2px 0;
    float: left;
}

.multiSelect a span {
    float: left;
}

.multiSelect a i {
    float: left;
    display: block;
    margin: 2px 0 0 2px;
    border-radius: 2px;
    width: 8px;
    height: 8px;
    padding: 4px;
    position: relative;
    -webkit-transition: all .3s;
    transition: all .3s
}

.multiSelect a i:before, .multiSelect a i:after {
    position: absolute;
    left: 8px;
    top: 2px;
    content: '';
    height: 12px;
    width: 1px;
    background-color: #fff
}

.multiSelect a i:before {
    -webkit-transform: rotate(45deg);
    transform: rotate(45deg)
}

.multiSelect a i:after {
    -webkit-transform: rotate(-45deg);
    transform: rotate(-45deg)
}

.multiSelect a i:hover {
    background-color: #545556;
}

.multiOption {
    display: inline-block;
    padding: 0 5px;
    cursor: pointer;
    color: #999;
}

.multiOption:hover {
    color: #5FB878
}

@font-face {
    font-family: "iconfont";
    src:
        url('data:application/x-font-woff;charset=utf-8;base64,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')
        format('woff')
}

.iconfont {
    font-family: "iconfont" !important;
    font-size: 16px;
    font-style: normal;
    -webkit-font-smoothing: antialiased;
    -moz-osx-font-smoothing: grayscale;
}

.icon-fanxuan:before {
    content: "\e837";
}

.icon-quanxuan:before {
    content: "\e623";
}

.icon-qingkong:before {
    content: "\e63e";
}
</style>
`<div class="layui-inline">
                      <label class="layui-form-label">商品类别:</label>
                      <div class="layui-input-block">
                       <select id="categoryCode" name="categoryCode"  multiple >
                               <option value=""></option>
                               <option value="30">30_烟酒水饮</option>
                               <option value="31">31_休闲食品</option>
                               <option value="32">32_冲调食品</option>
                               <option value="33">33_粮油调味</option>
         </select>
                      </div>
                 </div>