动态隐藏DIV层的问题

<script language="c#" runat="server">
public void aaa(object src,EventArgs e)
{。。。
}
</script>
<form runat="server">
<div id="div1" runat=server style="visibility:hidden ">abckd;
 </div>
  <asp:button Text="aaa" runat="server" OnClick="aaa"/>
  </form>

div1.Styles["visibility"] = "visible";