<style>
    .file-group {
        position: relative;
        width: 200px;
        height: 80px;
        border: 1px solid #ccc; /* 为了显示可见区域，非必须 */
        overflow: hidden;
        cursor: pointer;
        line-height: 80px;
        font-size: 16px;
        text-align: center;
        color: #fff;
        background-color: #f50;
        border-radius: 4px;
    }
    .file-group input {
        position: absolute;
        right: 0;
        top: 0;
        font-size: 300px;
        opacity: 0;
        filter: alpha(opacity=0);
        cursor: pointer;
    }
    .file-group:hover {
        background-color: #f60;
    }
</style>
<div class="file-group">
    <input type="file" name="" id="J_File">
    选择文件
</div>