Theme problem on changing the Zoom level of the monitor

Hi, I am facing this problem.Whenever i change the zoom level of my monitor,ideally the screen theme should accomodate with it but in my case, the left menu and the right content is zooming out(getting small) aND THERE IS THIS SPACE PRODUCED BETWEEN BOTH MENU AND CONTENT. I have used a split panel and locked the splitpanel left menu at 8%. I thought the percentage would accomodate the monitor screen perfectlybut is not. Kindly help ASAP.