Three cards layout using pure CSS and flexbox/grid

I wanted a small and fast project to have fun today and this one was great.

• I use only pure CSS.

Maintainability:

• I borrow some tips from BEM without doing full BEM. I only use someting useful for maintainability : separation of css features.
• I use variables for a better maintainability too : I need only to change these variables.

Design:

• I try to maintain size to improve the design rule of consistency : I used multiple of 6 (font-sizes) and 8 (white spaces).

Performance:

• I customize my own reset.css as I didn't want to made useless rules for this project.
• I may have done css in only one file (for performance reasons) but to better organized css I separate css files and comments to search easily inside css files (with cmd or ctrl+F).

Questions:

• You can also help me to find a better way to use flexbox and grid: what can be improved ?
• I try to follow "DRY" but tel me if I can do better.
• And every other advices for best practices are welcome to improve myself.

I have done nothing for accessibility (aria-label etc.), I can improve this later.

Have a good moment discovering my project. :)