Four card feature section with HTML and CSS

My sizing is a little off from the design jpg. I felt like I did a lot of guessing trying to get padding/margin between elements right. Any tips on "guessing" the design dimensions? I assume the answer is that it will get better with time...

Go easy on the footer lol. I was lazy on the attribution section. I couldn't get it to stick to the bottom the way I wanted and realized as I am submitting this that I never came back to it.

Any tips for code cleanup, or best practices would be appreciated :)