Hi @partyk1d24 
Great questions! At this time, we do not have “calc” or “flexbox” support. But it is something we are looking to implement in the future. if you have time, please make a new thread about it on our “Wish list”: http://forum.webflow.com/c/feedback/wish-list
Also, you can always put your own custom CSS/code in the head tag (http://help.webflow.com/site-settings/custom-code) or export the code and do what you want with it (http://help.webflow.com/features/exporting).
Hope this helps