First you must set the html- and body-tag to height: 100%:
html, body { height:100%; }
And second: you need to change the position of the first div as "relative" and not "absolute" (as in the jsfiddle file):
position: relative;
Hope this helps ...
EDIT: And delete <br> -Tag between the two divs - if not, there will be a white gap between them ...
source share