QR-code adjusted for mobile and desktop

Definitely need to get more practice of "coding flow". I mean I have to understand better how to code adherently, logically, methodically instead of coding jumping from one part of the project to another, making some small changes here and there.

Also, I would like to get some hint or help with getting rid of extra empty space below my text elements when screen size is 800px+ - once I set the screen size (in Chrome DevTools) to 800px empty space appears below my heading and paragraph