How do I remove the black bars on the top and bottom of app

Hello. I export my app as html and put it in Dropbox and when I view it on a mobile device I get black bars on the top and bottom of my screen. I read some tutorials on how to support multiple screen sizes, but none of them remove the bars. Is there a setting I need to change? When I change the "Fullscreen in Browser" from "Letterbox Scale" to "Scale Outer" the bars are gone but the objects are large and off-center. Does anyone know of a tutorial that might help?

It would be useful if I could just do something like "Set canvas size to Device.Width x Device.Height" Is there anything like this?

Thanks for the help!

If you've read the tutorials on supporting multiple screen-sizes, you must have also read the pros and cons of each..

Depending on how you have your game set up, you choose the "Fullscreen in Browser"-option that suits you best and make the nescessary adjustments to make it look the way you want..