Mobile first using vanilla CSS/HTML, no SASS

This is my first crack at web design after doing some free online courses. I mainly used flexbox for alignment and centering. I found the main card design very straight forward to do, although I was stuck on the background circle images for hours.

At first, I embedded img tags in the HTML and positioned them relatively via CSS. But I found this created little scroll bars/space and made the images and site non-responsive, I couldn't figure out via this method how to make them size dynamically. So in the end, I used pseudo before and after elements on the main container and background code and that worked. Any suggestions would be much appreciated :) Many thanks Steve