<input type="button" value="改变颜色" onClick="a1()" />  
    <input type="button" value="改变宽高" >
    <input type="button" value="隐藏内容" >
    <input type="button" value="显示内容" >
    <input type="button" value="取消设置" >
  </form>
  <script type="text/javascript">
//定义"改变颜色"的函数
    function a1{
        var a1=document.getElementById("con");
        a1.style.color="red";
        var a2=document.getElementById("txt");
        a2.style.backgroundColor="#CCC";
    }
为啥不能生效