First Project Ever - QR Code Using Basic HTML and CSS

Specifically for sizing and positioning the divs, is there a better, best-practice way I could have written those lines of code?

This was my very first project that a tutorial wasn't telling me what to do step-by-step. My biggest challenge was figuring out the best-practice way to structure the CSS. I got the design looking the way I want, but I'm not sure if I did it in the best way possible. Please note, there is not responsiveness in this code as I have not gotten to that part in my lessons yet. Optimization is on the way!