Responsive 3 column preview card component using Flexbox and Sass

I would appreciate any feedback or tips.

Specifically, I'm wondering how I did on my mixins and media queries. I struggled a lot with the phone layout.

Why isn't my background color working?

I thought I'd give utility classes a try for margins. It worked, but I'm not sure if I should have used them in this case.

Also, I'm looking for any feedback on how I could make my code better, prettier, more efficient, and up to date. I tried to keep accessibility tips from my last challenge in mind, so we'll see how I did this time.