jmerrill's post in How to Target Just "Wall" Summary Blocks for CSS Edits was marked as the answer
@Ziggy Thanks but didn't work. Found out from @inside_the_square that the selector is actually: .sqs-gallery-design-autocolumns. Tried it, it works!
jmerrill's post in How to Add Titles to individual images within a Gallery Block was marked as the answer
Never mind - I figured it out.