Forum Moderators: not2easy
How does this happen? is it because of CSS? How can I create something like that?
In FireFox take a look at the Web Developer extension for some page dissecting tools. I'm sure there are other extensions that will assist you in the effortless lifting of images off any page.
For example, [forums.mozillazine.org...] (Firefox support forum) uses CSS to display sky.png and blimp.png in the masthead.
In Firefox, I go to Tools > Page Info and select the Media tab. From there, I can see and save both images.