img.liuyifei.net 
This causes the blank white screen problem. The page is totally blank until the stylesheet at the bottom is downloaded, on the order of 6-10 seconds for this page. The browser is waiting for the stylesheet to be loaded before it renders anything else in the page, even the static text.
导致的问题就是，页面会有一段时间“朴素”，突然之间又“华丽”，用户体验很不好。
2、尽量使用
This is a valid syntax, but, even though it's in the document's HEAD, it breaks progressive rendering and instead causes the blank white screen and Flash of Unstyled Content problems.
