input file set style

css:

#file{
position: relative;/*设置input父元素*/
}
#file input{ 
position: absolute;
font-size: 100px;
right: 0;
top: 0;
opacity: 0;
bottom:0;
filter: alpha(opacity=0);
cursor: pointer

}

html:

 <div id="file">
  <input type="file"  id="fielinput"/>
 </div>