Masonry Captions Padding or Centering on Mobile

I want to add padding to the left and right sides of the captions not the image in mobile only (see image), but I can't seem to do it without adding padding to the image as well. It's a Masonry Grid. The text was added in the description of each image. 

Any help would be appreciated, I have added a screenshot of the other custom css I have added. (I'm a noob with coding so I may need to add/change something in what I have already)

thanks!

Can you share link to page where you use masonry? We can check easier