Hey, sorry to keep you waiting!
Degrees don’t really make sense online (since you don’t have control over the screen size and viewing distance of your participant), so they haven’t been implemented properly. Pixel and height units do work. I you would like to exercise more control over the size of the stimuli, see Wakefield’s Crib Sheet for a calibration method. PsychoPy Python to Javascript crib sheet - Google Docs
Best, Thomas