Four card feature section Solution

You are right, but I'd recommend using rem over em for the font-size. When using em for font-size the value always refers to the elements parent font-size and calculates its size according to it. Using rem (abbreviation for root-em) always looks at the root element (html-tag) and calculates its size from there. (Remember: Using em for margin and padding always refer to the actual elements font-size, not the parents.)

This makes it easier if you want to change the font-size in media queries because you mostly just need to change the html's font-size and all the other font-sizes scale accordingly. The parts where you actually need to manually adjust the font-sizes will be a lot less using this approach.

Nice work on this challenge! As @AlexBueckig mentioned, I'd also recommend rem over em, it's much easier to control. Even though the style-guide.md mentions 15px for the regular text, I'd still size it in rem. The 15px is just there as a reference.

I hope you enjoyed the challenge!