Glowing effect in themes?

Can somebody give a simple overview of how to add a glowing effect to an existing theme? I know it involves bloom, but after messing with the theme editor for an hour, I can’t seem to find the right settings to make the lines get that glowing effect.

Also, when you’re in the theme editor, and you click on an element (like “line renderer”), I see that it highlights the relevant part of the Vital UI, but I don’t see how you would know which of the many colors is associated with that element. Usually when I open a theme, there might be 20 very similar colors in the theme, so it’s hard to know exactly what color to edit if I want to change the color of a specific element.

I know these are very basic questions, but theme editor documentation is very sparse.