I showed you how to centre properly in your other thread. The code I gave you was centred in the window at any size. The code from your link is a mix mash of magic numbers and old techniques and I would steer well clear from it.)
The image you show above is just a fixed width and height element in the centre of the window with overflow set to allow the inner content to scroll.
If you use the fixed width version then you would need media queries for small screen as obviously they are smaller than the fixed width stipulated. I used percentages in my demo.
You keep using that website as a reference but its not a very accessible website and uses a lot of bad practices. Indeed it keeps crashing for me.
I would urge you to take a course on flexbox/css and then you can make your own designs at will. We can help you with CSS/flexbox and layout issues and arrangements but we can’t build a whole site from scratch for you