Put JavaScript and CSS in an external file

1, in the real world, the use of external files will speed up the page display, because the external files will be cached by the browser. Improved reusability of script files and style sheets. (Do not need to be defined once per page)

2, reduce the page volume, can improve the page loading speed. (script files and style sheets can be cached separately by the browser)

3. Improve the maintainability of scripts and styles. (although this is not performance-related, but it is also very important)

**_base.css **.common.js

Put JavaScript and CSS in an external file