Update: Here’ a solution based on a CSS ID, in this case “#rpwe_mystyle”. Please critique if there’s a better way:
1. Add a style definition to the main style.css of your child-theme e.g.
#rpwe_cdasr.rpwe-block h3{
...include all the plugin's attributes...;
font-weight: 700;
}
2.In the [rpw] shortcode, include “cssID=rpwe_mystyle”