Add attribute: controls just to refer to the standard control-pannel of each browser or build them on your own, as you want them to be for each viewport-screen/device!
* {box-sizing:border-box} will fitt padding, margin and border in total width: raccomanded
* is universal selector so apply in each, if fixes bad on other pages belive you could just put it a new external or internal reference or even inline as just command.
Should work out