here is what I did. It may not work exactly as-is in your situation, but it should get you started...
1. create a new page template (I called mine "user_editable_css")
- the template looks like this
{process_pagedata}
{content assign="content_var"}
{literal}
div#content2 {
background-color:
{/literal}
{content block="RightDivBackgroundColor" oneline="true"}
{literal}
}
{/literal}
2. create a page (I used page alias = editable-css), and assign it to the template you created above. This page will be the page that the user edits to change the selected styles (per the content blocks you put in the template).
3. in your regular page template(s), add this between the head tags:
That's it! Now you can edit the editable-css page, and see your changes immediately on any page that uses the template(s) you modified in step 3.