div层被下其他控件覆盖的完美解决方案(下拉列宽)

<li class="list1"  onmouseout="document.getElementById('divlist3').style.visibility='hidden'"  id="LCrm_Message" >//更具鼠离开或者移上来控制是否显示
                <a href="Pages/Default_Left.aspx?id=2" target="left" id="ACrm_Message" class="white">园区导航</a>
                  <div id="divlist3" style="position:absolute; visibility:hidden; left:0px; "> //开始控制
                  <ul id="list3">
                     <li ="none3()"><a href="Pages/Default_Left.aspx?foc=7&id=2" target="left" class="fir" id="A23" />                      <li ="none3()"><a href="Pages/Default_Left.aspx?foc=3&id=2" target="left" class="fir" id="A19" />                      <li ="none3()"><a href="Pages/Default_Left.aspx?foc=1&id=2" target="left"  class="fir" id="A3" />                      <li ="none3()"><a href="Pages/Default_Left.aspx?foc=5&id=2" target="left" class="fir" id="A21" />                      <li ="none3()"><a href="Pages/Default_Left.aspx?foc=4&id=2" target="left" class="fir" id="A20" </li>
                     <li ="none3()"><a href="Pages/Default_Left.aspx?foc=6&id=2" target="left" class="fir" id="A22" </li>
                     <li ="none3()"><a href="Pages/Default_Left.aspx?foc=2&id=2" target="left" class="fir" id="A4" </li>
                     <li ="none3()"><a href="Pages/Default_Left.aspx?foc=9&id=2" target="left" class="fir" id="A25" />                      <li ="none3()"><a href="Pages/Default_Left.aspx?foc=8&id=2" target="left" class="fir" id="A24" </li>
                     <li ="none3()"><a href="Pages/Default_Left.aspx?foc=10&id=2" target="left" class="fir" id="A26" </li>
                     <li ="none3()"><a href="Pages/Default_Left.aspx?foc=17&id=2" target="left" class="fir" id="A33" </li>
                     <li ="none3()"><a href="Pages/Default_Left.aspx?foc=18&id=2" target="left" class="fir" id="A34" />                      <li ="none3()"><a href="Pages/Default_Left.aspx?foc=11&id=2" target="left" class="fir" id="A27" />                      <li ="none3()"><a href="Pages/Default_Left.aspx?foc=12&id=2" target="left" class="fir" id="A28" </li>
   
                 </ul>
                 <iframe style="position:absolute; visibility:inherit; top:40px; left:2px; width:143px; height:416px; z-index:-1; filter='progid:DXImageTransform.Microsoft.Alpha(style=0,opacity=0)';"></iframe> //ifram设置它的高度可宽度来控制大小。因为ifram的级别大于下拉列宽的级别
                   </div>//结束控制
            </li