Hi, the problem is that inside #container, the columns are floated. That makes the parent not recognize them, aka it thinks that it’s going to the 100% height!
You’re welcome sir :). And if you ever need to “contain the floats” (as overflow:hidden is doing right now for you), and you need a design element hanging out of the container, look into using the “clearfix”. You can google that if you want, to read up on it, but overflow:hidden is good for 99% of cases.