Responsive page using BEM with CSS Flexbox and Media Query

I started learning web development just 1 month ago, so keep in mind that I'm quite a beginner. I'm focusing on learning the basics and I tried to apply the BEM methodology in the construction of CSS, it seemed the simplest to apply for a beginner and I hope it turned out good. If you are more experienced and have any tips to give me, don't hesitate to send me a message, I love to learn.