Responsive 3-column challenge

Hello again. This is my second attempt at this challenge. My first attempt was completed shortly after learning basic CSS, so it lacked any responsive elements. Since then, I started learning bootstrap, so I decided to try this challenge again. I believe I did well on the visual side of this website, but I wonder how well I did on the responsive side of the page. Question:

1. I used @media to do the transition for the border corners. It "seems" to have worked, but I wonder if it is efficient.
2. I had to use many classes to do the fine-tuning. Could you give me some tips for how to consolidate the use of classes?

Thank you!