Mobile content width

Adding what you want to the media query(s) in your stylesheet should do the trick!

Ex. If you want it to go when the screen width is 320px wide:

@media only screen and (max-width: 320px) {
#maincontentcontainer {
margin: 0;
border: none;
}
}

Hope that helps!

Thank you, seems simple enough. I will try it out.

Since posting this I am no longer able to edit CSS? I get a white screen when I update file.

Oh no! Are you editing the file using the wp editor?

Yes I am.

Ok, I edited the file outside of the editor and that worked. Thank you!