待参考

http://www.runoob.com/tags/html-httpmessages.html   http消息

http://www.runoob.com/tags/html-httpmethods.html     http方法

http://www.runoob.com/tags/ref-pxtoemconversion.html      px和em换算公式

http://www.runoob.com/tags/html-keyboardshortcuts.html    键盘快捷键