The google map dimensions have to be in pixels. And it's 2016.
If I enter "100%" for the width, it renders as "100%px". If I put "15rem" for the height, it renders as "15rempx". Secondly, it renders the dimensions as *inline style*, which is impossible to override in CSS without using an UGLY and messy !important suffix.
That's as far as the problem description goes.
As for the solution:
Remove the fields. Done!
These things should be in CSS anyway. They have no place in the HTML, *especially* not as inline style.
If you absolutely *have* to have these fields for whatever odd reason, please do no append "px" to them internally. If a different unit is entered, leave it be, and don't render it as invalid CSS.