Navigation Column running into main frame for Mondrian

I'm using the Mondrian template. Whenever the browser window is minimized and one needs to scroll over horizontally (or, on a smart phone/tablet screen the website is zoomed in on) the navigation column on the left stays put, and the text runs into main content. How do you have the navigation column integrated with the main site?
Site is http://linexlineproductions.com/. Thank you