Mobile-first landing page, using semantic HTML and CSS

I've been trying some BEM techniques in this project, but I think it needs some work. I feel a bit silly that I haven't fully got my head around how to implement BEM properly; if anyone has any pointers then please let me know!

With that, I would love to hear any pointers with regards to how I could make my HTML more semantic! No doubt that there will be areas in which I could improve on this.

Thanks for checking out my project :) Have a good day!