Thanks for the reply Gary, however I don't think it is a good idea to be beholden to a theme for such elementary styling. I think the "Additional CSS Class" field under "Advanced" points to a good way to handle this, but I don't want to be bouncing back and forth between Gutenberg and the Customizer's CSS panel. Worse yet the Customizer's CSS panel is also quite inadequate. Should not Customizer/Gutenberg be at least as good at CSS as https://beefree.io or https://mosaico.io or several others like them?