How can I reorder my divs using only CSS?

Question

Given a template where the HTML cannot be modified because of other requirements, how is it possible to display (rearrange) a div above another div

Answer 1

CSS really shouldn't be used to restructure the HTML backend. However, it is possible if you know the height of both elements involved and are feeling hackish. Also, text selection will be messed up when going between the divs, but that's because the HTML and CSS order are opposite.

#firstDiv { position: relative; top: YYYpx; height: XXXpx; }
#secondDiv { position: relative; top: -XXXpx; height: YYYpx; }

Where XXX and YYY are the heights of firstDiv and secondDiv respectively. This will work with trailing elements, unlike the top answer.