remove blue background color on mobile browsers (#4426)
remove blue background color on mobile browsers (#4426)

* remove blue background color on mobile browsers

-webkit-user-select was removed in new Chromium / Blink versions

https://www.chromestatus.com/feature/5062926088011776
https://www.chromestatus.com/feature/5722186220306432

http://caniuse.com/#feat=user-select-none

* use transparent

* Remove unnecessary vendor prefixes

Dogfalo/materialize,tomscholz/materialize,ZiperRom1/materialize,Dogfalo/materialize,INGCRENGIFO/materialize,ZiperRom1/materialize,INGCRENGIFO/materialize,digitalkaoz/materialize,ccloli/materialize,tomscholz/materialize,ccloli/materialize,digitalkaoz/materialize