Paddings and Margins to Apply To Desktop and Not Mobile

I need to be able to change the padding and margins for the desktop version of my site, but not have them apply to the mobile version.

The reason I need to do this is because when I set my columns to 1/3 + 2/3, for example, my content is too close to the border of the website on the left side. I need to add margins to move the content in by about 100 px. On mobile, this shifts everything so that part of the content is off the screen on the right side.

I also have to use margin and padding augmentations for my testimonial boxes when I have my columns set to 1/3rds. Otherwise, they are not properly spaced on the desktop version. When I do that, however, my mobile version is totally off-centered.

Is there a way to have margins and paddings that do not go through on the mobile site? I don’t see a place to add CSS under Column Settings. I’ve tried the Responsive Options to no avail because what I’m doing involves padding and margins not columns.

Thank you for your time.