How to target only one element if more elements share the same CSS class

I don’t know how comfortable you are with development, but it is possible to do what I think you’re asking.

Option 1: Customize the theme templates to apply a different class to the first item. Requires some WordPress templating and php know-how.

Option 2: Use css pseudo classes to target the first image with that class and give it different styles (something like .yourclass:first-child{ border: 1px solid red; } ). Requires some css/less/sass know-how (not sure how the theme is set up). Without seeing a sample page I can’t tell you much more than that.