YUI中的css——Grids.css

1，grids.css中頁面布局的寬度用的是em寬度，是因為em會隨著用戶調整字體的大小(查看-文字大小)而改變寬度，從而有更好的用戶體驗；

2，根據reset.css，頁面字體大小為13px，所以頁面寬度也要根據13px來設置em，但是，在ie中有點問題，如果在firefox等標準瀏覽器中字1em為13px的話，在ie中要13.3333px，而且用*過濾器來設置ie中的em寬度。如在body字體大小為13px的情況下設置頁面寬度為600px，在ie中為45.00em，而在firefox等標準瀏覽器中為46.15em。

3，注意(來自http://developer.yahoo.com/yui/grids/)

   Here are some other things to keep in mind: 1) The width is set in ems because ems scale with user-initiated font-size adjustment, and therefore provide a superior user experience. 2) YUI Fonts does a good job of normalizing the width of an em, but we're still obliged to provide a slightly different value for IE. 3) Be sure the width value for IE comes after the value for everybody else. 4) Setting the min-width is optional, but helps the grid maintain integrity as the viewport shrinks. 5) The text-align and margin are used to help center the page, and should not be modified.