Making the absolute, relative

A curious reader recently asked about the Adaptive Path redesign:

“I’m puzzling over why with the main nav bar you nested an absolute div into a relative div?”

A simple answer to his question is: Because I wanted optimum flexibility for the header and navigation, and to keep the navigation the same distance from the logo, no matter how the text is resized.

That’s the strategic answer providing rationale for the method. But I gather he might also be seeking a tactical answer. To answer his question thoroughly, I’ll backpedal a bit, and explain the workings of CSS absolute positioning in my own words, provide an example which demonstrates a different effect than the one achieved in the Adaptive Path design, then come back to the AP navigation.