With JavaScript you can change the CSS file a page uses without requiring a page refresh.  I have used this technique many times on non-SharePoint sites but there are some special challenges implementing this in SharePoint.  For this solution there were several requirements.

• Users need to be able to switch themes and have the setting saved
• No page refresh
• Should be able to use both out of the box themes and custom themes

So first I needed to get the CSS files and images for the themes I wanted to use.  When you assign a theme to a site all the files for the theme are copied to a folder named _themes in the root of the site. 

_themes folder

So what I did was assign each theme I wanted to use to the site one at a time.  With SharePoint designer I copied the files folders for each theme into a document library called Site Styles.  Each folder contains all the resources needed or the theme to work. 

Here is what I ended up with

Site Styles Library

If I wanted to create a custom theme I could just add another folder with my custom CSS and images.

This same technique can be used when developing your own custom theme, just copy one that is similar to what you want and use the alternate CSS link on the master page settings page to add it to the site.  Inside of the folder for each theme is a file named theme.css. Link to that file and SharePoint will apply the theme to the site. 

Alternate CSS URL

Now everything we have done so far is pretty basic and easy to do but we will pull all this together with some simple edits to the master page to complete the solution. In part 2 I’ll explain how we use JavaScript to switch styles and set a cookie to remember the users theme choice.

Related posts:

1. Switch Themes Without a Page Refresh: Part 2
2. Adding references to the page head: the easy way
3. Styling the MOSS horizontal navigation menu