Displaying a web page that fits the users screen is vital. Realistically, you need to render your site for a smartphone and as high as 1920px!
That’s a huge range, and the number of options to do this is thankfully increasing.
Adapt.js is a lightweight option that decides which CSS file to load based on the users screen size. This handy cup of JavaScript is built with the 960 Grid System, so if you’re familiar that, implementing Adapt.js should be fairly natural.