上传文件input（type=file）美化。

input file 把之前的按钮透明度opacity设置为0，外层用div包裹。

<div class="uploadButDiv greenButton text-center">
　　<input type="file" accept="image/jpeg,image/jpg,image/png,image/gif"/>上传
</div>

.uploadButDiv {
    width: 100%;
    height: 3.25rem;
    line-height: 3.2rem;
    position: relative;
    cursor: pointer;
    color: #0057FF;
    font-size: 1.125rem;
    background: #fff;
    border: 1px solid #0057FF;
    border-radius: 4px;
    overflow: hidden;
    display: inline-block;
}

.uploadButDiv input {
    width: 100%;
    position: absolute;
    right: 0;
    top: 0;
    opacity: 0;
    cursor: pointer
}