Custom Css for elements within Page Builder Widget

Hi, can someone perhaps refer me to the documentation on this? I’ve tried reading previous threads and I don’t seem to be getting the hang of it.

I want to amend styling for text elements within a widget.

EG I have an H3 title, and the stylesheet for my theme is styling that with a margin-top: 20px

For this instance of use of H3 I want only a margin-top: 5px

I’m guessing there is a way to use the Attributes drop down in the right column to achieve this, but I can’t figure it out.

Thanks

Chris