怎么样才能让Button显示为按下时的样子

<style type="text/css">
<!--
.sty1 {  border: 2px inset}
.sty2 {  border-style: outset}
-->
</style>
<SCRIPT LANGUAGE="JavaScript">
<!--
function changeSty(){
  if(document.all.b1.className=="sty1")
    document.all.b1.className="sty2"
else
document.all.b1.className="sty1"
document.all.b1.focus();
}
//-->
</SCRIPT>  <input type="button" name="b1" id="b1" value="按钮" class="sty1">
  <input type="button" name="Submit2" value="切换" onclick="changeSty();">