Does anybody know what causes the following problem?
When (near litteraly) following Bucky's great course (thanks a million Bucky, it has been fantastic so far), I bump into a strange problem.

I have succesfully made beautiful nav-bar (with inline blocks), but when editing the <section> part, nothing seems to work (changing background color, float, etcetra). Changing the <aside> works fine (background color, float, etc). 
I have tried changing <section> into <div>, and removing section and giving the <article> an ID and changing that float, but that doesn't work either. Does anybody know what I am doing wrong?