I set up my whole site with another theme (Apex) and formatted the content into columns using this code:
Then I switched the theme to GeneratePress because I liked many of the features. However, what used to format correctly not longer does. No matter what width I set the layout to (even max of 1500) all the column text ends up stacked vertically.
I asked a friend who is a css coder to look at it, and he wondered if the theme was broken, ie the browser sniffer incorrectly resizes my pages’ content to tablet mode.
You can also make use of the built in CSS framework in GeneratePress, but doing so will lock you into GP, and if you switch themes again, you’ll need to switch the column codes again. If you’re interested, you can learn more about it here: http://unsemantic.com/