Question: According to this quirksmode article, <http://www.quirksmode.org/css/display.html> 

> 
> A block has some whitespace above and below it and tolerates no HTML
>  elements next to it, except when ordered
> 
> 
> 

Are the whitespace above or below stated in pixels or is it just 'whitespace'?.

Answer: 
In the given context, "whitespace" is a gross misnomer. Whitespace in terms of text should *never* directly interfere with the layout of non-inline block boxes; what you should see between block boxes are *margins* (usually of said boxes), which are completely different.

Margins are indeed stated in pixels. In fact, they may be stated with any CSS length unit; see the [`margin` properties](http://www.w3.org/TR/CSS21/box.html#margin-properties) in the spec. You don't specify a pixel length for whitespace directly for elements that flow inline; that is usually controlled by `font-size` instead, but when working with block boxes that should be entirely irrelevant.
The 'whitespace' is the element's margin and can be controlled via any standard CSS unit (e.g. px, em, %, etc.)