(The picture is large. Internet Explorer & Mozilla 1.3 users can press F11 to toggle between normal and full screen)
A stylesheet is used to control the appearance of the default template pack that ships with 4images.
It governs things such as table background colors, etc.
If you are unfamiliar with stylesheets, here is an excellent reference:
http://webdesign.about.com/cs/css/This is a picture of how templates/default/style.css is used
There are more classes and selectors used than are pictured above.
If you open style.css in a text editor, you will find comment lines such as:
/*--Categories------------------------------------------------*/
/*--Images----------------------------------------------------*/
/*--Comments--------------------------------------------------*/
These identify the blocks of css code that work with Categories, Images and Comments.