Review my website

Hi everyone.

Not sure in which category I should post this, but I recently started a new project to practice my html and css skills (still a beginner). I created a website (just a landing page) from scratch and tried to make it somehow responsive for mobile devices. However I struggled a lot with the responsive design, so if anyone has some tips or advice on how to do it better or mistakes I made, please let me know below. I really want to learn and become better.

Github link: