This is a buggyfill (fixing bad behavior), not a polyfill (adding missing behavior). That said, it provides hacks for you to get viewport units working in old IE and Android Stock Browser as well. If the browser doesn't know how to deal with the viewport units - vw, vh, vmin and vmax - this library will not improve the situation unless you're using the hacks detailed below. The buggyfill uses the CSSOM to access the defined styles rather than ship its own CSS parser, that'S why the hacks abuse the CSS property content to get the values across. The buggyfill iterates through all defined styles the document knows and extracts those that uses a viewport unit. After resolving the relative units against the viewport's dimensions, CSS is put back together and injected into the document in a <style> element. Listening to the orientationchange event allows the buggyfill to update the calculated dimensions accordingly.