Huddle landing page using HTML/CSS

This being my first Jr. level challenge, I had a few difficulties. One of them being that I was not able to make my pictures inside my Sections in the main smaller, making the images look really big. Another roadblock I encountered was that of the container that goes in between the footer and the main. I wasnt sure if what I did was best or if I could have used Flexbox on the whole page to position it better. Feedback on my code would be greatly appreciated, thank you.