Responsive testimonial website

I should of gone mobile first on this project. I think that was my biggest mistake. Overall awesome experience. I struggled the most with the Javascript this time. I got the code to do what I wanted it to do. I just dont understand why it actually works. For my next project i really want to stop building and watch some best practice videos on refactoring and best practice. I also dont really use flexbox or grid as much as i think i should? Im not sure give me your thoughts on how you would of done this project or just some awesome feedback would be nice! have a good one!