Ask HN: CSS framework for rapid prototyping?

Most of the CSS frameworks I know let you to set the grid, the typography and few other things. It frees your mind from browse compatibilty issues, but you still have to worry about the actual design of the page, what costs a lot of time in case of rapid prototyping for purely experimental purposes.

Is there a CSS framework that contains a set of CSS rules for commonly used UI elements, like forms, buttons, navigation, user navigation and such, so you can work on the actual interface immediately?