Styling blocks

I’m trying to build a page in Gutenberg (5.2.4, not 5.3 yet), and I’m running into a rather frustrating issue. In my page mockup, I have a header, footer and 3 separate sections for the body. The problem is that my 3 sections all have different background colors, but if I try to add classes to my blocks so I can target them to add background, that color does not extend to the edges. There appears to be a stack of wrappers around each block that cannot be classed or modified through the editor. How am I supposed to target these “wrappers” on a per block basis to apply background colors only to specific sections?

Here are some images to hopefully illustrate:
What I want: https://i.imgur.com/ea7ghFR.png
What I get: https://i.imgur.com/BJeiKbk.png

I want to do this in a way that does not involve plugins. I shouldn’t need a plugin to style some blocks. I’m curious though, when I assign a custom class to a block through the Gutenberg editor, why that class isn’t applied to the outermost WRAPPER?

Thanks for any help.