大部分遮蓋層都是通過JS去擷取高度和寬度來定位的，而現在採用的大部分是CSS去做，除了一個為了相容IE6所必要的js。
大致原理就是：讓遮蓋層的height和width達到100%來去實現，IE6下需要將body的height設為100%才有效。
具體的代碼如下：
<!doctype html><html><head><title>CSS 實現遮蓋層</title><meta charset="gb2312" /><style>/* the style for layer or mask */body{_height:100%;}#mask, #undermask{display: none;position:fixed;_position:absolute;top: 0;left: 0;width: 100%;height: 100%;z-index: 33;background-color: #101010;filter: Alpha(opacity=40);opacity: .4;}/* page show */#page{width:960px;margin:0 auto;height:1000px;text-align:center;background-color:#c00;}</style></head><body><div id="page">)))))))))))))CSS 實現遮蓋層測試(((((((((((((((</div><div id="mask"></div><script>(function(mask){// for IE 6if(document.uniqueID && !window.XMLHttpRequest){document.getElementsByTagName('html')[0].style.overflow = 'hidden';}mask.style.display = 'block';})(document.getElementById('mask'));</script></body></html>
就是這樣，很簡單明了。
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