Results summary component | How to properly scale? | Variables ?

Hello everyone! No major difficulty in recreating this page, but I have a recurring issue that I would like to solve. How do I properly adjust the size of the HTML? In the example, the mobile version was supposed to take up the entire page, and the desktop version was supposed to be centered. However, it seems like the size of my HTML file is limited. I think the solution is simple, but I prefer to ask!

Another concern, I'm a bit confused about the use of h1, h2, h3. Is it based on the importance of keywords on the page? Is it okay if they are out of order in the page chronology? (e.g., h1 > h4 > h2)

And one last question, when I wanted to change the color of the "reaction" block for example, I was looking for a way to take the variable used to color the text and just reduce the alpha of that variable for the background color. However, I can't figure it out. Any solutions? Thanks in advance!