CSS problem - equal the height of 2 divs

Hello, I have a simple problem with css and 2 divs. Bot of them must be expanding divs and must be of equal height. The problem is that one of them has different content and it changes its height on different pages, and the other must be the same height as the first. Very simple and easy job for the right person. If the project is done well, there are possible future projects. I'm looking to have this done in the next hours, so if you know what you are doing, do not hesitate to bid.