<style type="text/css">

a.btn {width: 120px;height: 42px;overflow: hidden;display: block;text-decoration: none;background: url(/images/chose_file.gif) left top no-repeat;}

/*file设为透明，并覆盖整个触发面*/

a.files input{ margin-left: -350px;font-size: 30px;cursor: pointer;filter: alpha(opacity = ); background:#;filter:alpha(Opacity=);opacity:;-moz-opacity:;filter:progid:DXImageTransform.Microsoft.Alpha(Opacity=);-MS-filter:"progid:DXImageTransform.Microsoft.Alpha(Opacity=0)";/*为了兼容各种浏览器*/}

    </style>

    <a href="#" class="btn">

        <input type="file" class="input_files" />

    </a>