The sky is the limit with CSS. These examples can be mixed and matched to radically change the appearance of your site.
There is one essential technique common to all of them, image embedding. For example, the header banner and background gradient on this page are both images inserted with CSS.
Before using these recipes, you need to create a place to store all the images. Create a new project, and call it something like "resources". Mine is named that (and you can find it here), but you can use something else. Leave the category field blank, so it won't appear in the sidebar. Upload all the various image files to this project, keeping them in one place for easier management.
Finally, in your
user.css file, link to the image with
resources/picture_name. The picture gets uploaded once, and every page will use it.