Webpage float issue

I'm usually good at css layouts but I'm having an issue. I have 2 sections, each left floated. The first column is a nav bar with a width of 140px, the second area I want to fill up and adjust according to screen size. The issue is that I want it to fill the rest of the area, but when I set a max width, say 85%, when I make the screen smaller, the div keeps the max size and just moves to under the nav bar. It's not actually dynamically shrinking off of screen size. Any ideas?

 

Nevermind I figured it out. I had widths set as well. But I just made the right content area not a float and put a left margin past the navbar. All good now.