After searching through lots of different discussions and questions and such, I ended up with a CSS code that both allows for widening the survey and widening a matrix table so that all of the options appear on screen (i.e., to avoid having to scroll to get to some of the options). 

The code that worked for me is the following (i.e., cut/pasted into the “Custom CSS” box under the “Style” tab on “Look & Feel”):

.Skin, .SkinInner {width:90% !important;}
.Matrix {max-width:100%!important;}
@media only screen and (min-width:1080px) {
 #Questions(min-width:1080px;}
}

I don’t know if there is a better or more sophisticated way to do this with CSS, but it worked and that’s all that I needed. Given the amount of effort I put into searching for the information to make this happen (and the number of people who seem to have this issue), I thought it worth posting what worked for me. 

Hopefully it helps for you (NOTE: this code is being used for a desktop/laptop only study, so I’m not sure what it means for mobile accessibility)