求解!!请问怎么改变动态按钮的背景呢？
<div style="left: 20px; margin-left: 50px; width: 273px; height: 21px"> <input id="S_btn" style="width: 38px; height: 23px; cursor: hand;" title="点击选择" type="button" value="S"/> <input id="M_btn" style="width: 37px; height: 23px; cursor: hand;" title="点击选择" type="button" value="M" /> <input id="L_btn" style="width: 37px; height: 23px; cursor: hand;" title="点击选择" type="button" value="L" /> <input id="XL_btn" style="width: 37px; height: 23px; cursor: hand;" title="点击选择" type="button" value="XL" /> </div>
<div style="left: 20px; margin-left: 50px; width: 273px; height: 21px"> <input id="S_btn" style="width: 38px; height: 23px; cursor: hand;" title="点击选择" type="button" value="S" onclick="setBackground(this)" /> <input id="M_btn" style="width: 37px; height: 23px; cursor: hand;" title="点击选择" type="button" value="M" /> <input id="L_btn" style="width: 37px; height: 23px; cursor: hand;" title="点击选择" type="button" value="L" /> <input id="XL_btn" style="width: 37px; height: 23px; cursor: hand;" title="点击选择" type="button" value="XL" /> </div> <script type="text/javascript"> function setBackground(o) { o.style.border = 'dashed 1px #ff8080'; } </script>