Change background color of input type file browse button

//css
.file_input_textbox
{
 float: left
}

.file_input_div
{
 position: relative; 
 width: 100px; 
 height: 23px; 
 overflow: hidden;
}

.file_input_button
{
 width: 100px; 
 position: absolute; 
 top: 0px;
 background-color: #33BB00;
 color: #FFFFFF;
 border-style: solid;
}

.file_input_hidden
{
 font-size: 45px; 
 position: absolute; 
 right: 0px; 
 top: 0px; 
 opacity: 0; 
 
 filter: alpha(opacity=0); 
 -ms-filter: "alpha(opacity=0)"; 
 -khtml-opacity: 0; 
 -moz-opacity: 0;
}

 
//html
<input type="text" id="fileName" class="file_input_textbox" readonly="readonly">
 
<div class="file_input_div">
  <input type="button" value="Search files" class="file_input_button" />
  <input type="file" class="file_input_hidden" onchange="javascript: document.getElementById('fileName').value = this.value" />
</div>