Adapt.js is a lightweight (848 bytes minified) JavaScript file that determines which CSS file to load before the browser renders a page. If the browser tilts or resizes, Adapt.js simply checks its width, and serves only the CSS that is needed, when it is needed.

A potential drawback of Adapt.js is the possibility of a brief flash of unstyled content as a new stylesheet is being fetched (think of it as “Ajax” for CSS). I have done my best to mitigate this by keeping CSS file…