Nowadays, websites can appear across hundreds of different screen sizes, even in different orientations on the same device (landscape or portrait).  The displays people see your site on can be just a few hundred pixels wide on mobile, up to thousands of pixels in width on newer hi-definition widescreen monitors.

Because new technologies provided a range of screen sizes that people can see your site with, it also required a new way of thinking about site design that made sure sites looked great on any screen…