As a very quick suggestion: those "540x960 XHDPI" etc options are not keyboard/screenreader accessible in their current form (with the display:none'd <input>)
On top of that, I strongly suggest the use of viewport pixels as a better reference.
XHDPI language is more for hardware geeks than front-end/css designers who go by pixels + dpr.
From https://lists.w3.org/Archives/Public/public-web-mobile/2015Jul/0002.html: