开发者修改css时不能更新更改的内容，这其实是浏览器中缓存的原因，这里拿firefox浏览器举例禁止浏览器缓存来解决这一问题的出现：
在地址栏中打about:config
在搜索中输入：browser.cache.disk.enable
选项解释：When a page is loaded, it can be cached so it doesn’t need to be downloaded to be redisplayed. For e-mail and news, messages and attachments are cached as well. This preference controls whether to use the hard drive for caching purposes. browser.cache.disk.capacity controls the maximum amount of disk space to use.
双击这个选项就可以更新修改的内容了。