修改上传按钮样式

<div class="head_portrait_b">		                         
   <img id="userAvter_pic" src="#" />
</div>
<a href="javascript:void(0)" class="btn_yellow">上传</a>
<div style="width:100px;position:relative; top:-23px; left:-15px;">
<input type="file" id="userAvter" name="avter" onchange="setPic('userAvter')" size="1" style="opacity:0; filter: alpha(opacity = 0); overflow:hidden; 

cursor:pointer; border:none;" />
</div>