Customization is achieved by modifying style attributes of HTML elements. Style sheets are arranged in four levels.

1. Your site has a default system layout style sheet, this is the one you selected when you creating your site.
2. Your site has a site-wide shared style sheet named _site.css. This file resides in your site's root folder. It is by default empty.
3. Each folder on your site contains a style sheet shared by all page in that folder, this file is named _common.css in that folder, it is also empty by default.
4. Each file has its own style sheet, named as name.css, where name is tbe basename of the html file. This file is also empty by default. 

The style sheets are loaded exactly as ordered above, with later style sheets override previous ones. This cascade mechanism gives a very flexible method to customize your site. You can do site-level, folder-level and page-level customization by using appropriate style sheets.

For most users, the only thing really need to customize is the banner images. They are used as background image of  HTML elements. There are two of them.

• The small banner image on the upper left corner of some layout templates. This image is of a fixed size   150x76  .
  
• The top banner image, of size  800x76 . This image is used in all layouts.
  

There are two methods to install banner images. Using the "Upload Banner Image" button on the admin screen or directly edit and upload the CSS file _site.css.

For those who want to use javascript in their pages. There is a similar arrangement of javascript files. The file _site.js is loaded by all pages on your site, the file _common.js is loaded by all pages in the folder, after _site.js, and the file name.js is loaded the last. All these files are empty by default.