Space between modular children

I am using theme inheritance to modify the default antimatter theme. I am creating a simple modular page. By default, the child pages of the modular page come with a lot of space (either padding or margins or something between them). I would like to reduce or remove this space. I have tried copying and modifying some of the scss files from user/themes/antimatter/scss to my own theme, but I can not figure out which files I should copy, and how to modify them (or even if the scss are the right files to modify). Any help would be appreciated.

I have figured it out!

I am using in my twig file <div class="modular-row callout"> and then in the template.css file, I can modify the .callout settings.

Next question: suppose I have a base set of css params in my .callout, how can I easily override them for just a single child of my modular page?

related: I am confused why modifying the _custom.scss file does not get picked up - I have to modify the template.css file - I'll keep poking around to see what I can deduce.

@walkloud:
related: I am confused why modifying the _custom.scss file does not get picked up - I have to modify the template.css file - I’ll keep poking around to see what I can deduce.

The answer is in the customization tutorial - what I did was OK (modify the template.css file) - if I would like to use the .scss files, I need to install a sass compiler, and learn how to use that. Probably, learning to use sass is better - also, I will check if putting my changes in the custom.css file gives the same result as modifying the template.css file - hopefully yes, as that would also be better than what I did.

EDIT: Yes - moving my changes from css-compiled/template.css to css/custom.css indeed works. NOTE - I am inheriting from the anti-matter theme which supports a custom.css file - not sure about other themes.

I'm trying to eliminate space between the modular sections on a page as well. I'm using the default Quark theme. I can't figure out exactly what to put in the twig file and template.css (or custom.css) file. Can anyone assist by posting the correct code?

Thank you