Stopping the CSS positioning panic (Part 1) « The CSS Blog, just CSS. (Tips, Tricks, Tutorials, Resources and more!)
http://thecssblog.com/tutorials/stopping-the-css-positioning-panic-part-1/

Best tutorial on css positioning that I've been

Nice example of a rounded corner menu

positioning

Absolute, Relative, Fixed Positioning

Finsta left a question in the forums: I am fairly new to web design and I could never master the differences in positioning of elements. I know there are

Absolute, Relative, Fixed Positioning: How Do They Differ? | CSS-Tricks

great article

centrar objetos en css

Centering an absolutely positioned element is a CSS challenge that occurs now and then. The solutions seem obvious once I’ve done it, but I still find myself googling the problem every few months.