Control 360 Survey Portal Rendering Width

Greetings -
I have a client where we need to use some custom css code to control the width of the survey when it renders in the survey portal and when it renders on the phone. I have played around with the custom css code for the look and feel but can't sem to figure out how to make is a max width and account for rendering on mobile.
The client wants to eliminate the amount of scrolling a participant has to do when they are complete a 360 survey in the 360 survey portal.
Help!!!
Thanks!
Alicia