3 Column Card using Flexbox and Grid

I'm having a better time structuring my code. One thing that I'm still confused about is the scale of the style guide. For this project, the font-size is stated as 15px, but when I use 15px as my body font-size, it doesn't look right... so I scale it higher, but then my preview image looks big and stupid.. lol. Anyways, aside from that, I think things are going smoothly!