background设成transparent时，IE10及以下会点击穿透
Bug: http://haiyang.me/demo/bgurl.html
Fix: http://haiyang.me/demo/bgurl_fix.html
之前我都是用一张1px的透明背景图片来修复这个问题，@钟玲 建议用#代替透明图片，赞~
<div style="background-image:url(#); position:absolute;z-index;99999; border:1px solid green; width:300px;height:200px;">This is cover layer.<br/>Click here won't through.</div>
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<button onclick="alert('click-events-passing-through')" style="padding-left: 150px;">I am below the cover.</button>