As Tor Haugen pointed out, the term "Object-oriented CSS" is a misnomer.
"Object-oriented CSS" is really just a design pattern for how to get most out of your CSS and is basicly the same approach Jonathan Snooks calls SMACSS.
Whether you call it OOCSS or SMACSS, the key to the approach is that you create generic UI elements like the nav abstraction. These UI elements can then be enhanced with more specific features by adding extra classes to the element and/or a container element. Or, as an alternative, you can add your own custom CSS rules using the element's ID or semantic classes.
For real world examples of OOCSS, check out frameworks like Cascade Framework, Scally and InuitCSS.
Further reading :
- An Introduction To Object Oriented CSS (OOCSS)
- OOCSS + Sass = The best way to CSS
