Coding Order Summary in Notepad without using Flex or Grid

Welcome. It is my first, and probably not the last (I hope :D) Challenge from this Site. I picked probably the easiest one just to look how this Site gonna work - how to submit challenges and how this gonna look. I just wanted to see the whole process from start the project and downloading the assets through the Coding the solution, and finally the end of this.

Did you remember your first website made on the IT class or even in home for yourself ? Did you started from Visual Studio Code, Atom, Notepad++ ? Or even Notepad ? Did you ever tried to code things in Notepad ? Because my first ametour website was written in this Windows tool. And because it is a very simple challenge I just wanted to go more hardcore and I tried to code it in one file (index.html) with just a Notepad. And yeah it was a little painful but also exciting.

Over that I gave myself one more challenge to this project - I wanted to do this without using flex or grid even if it is the easiest way to do some things even in that small project. I just wanted to test myself if I am creative and skilled enough to finish this in the old school way.

Even if I completed this and I am happy with that solution, I am still not quite sure about few things:

1. I tried to use semanthic HTML as much as I could but maybe I forgot or missed something ?
2. Did my CSS is readable enough or is it complicated as hell ? I tried to put styles as simple as I could, but maybe there is the way to optimize it ?
3. When we are at the CSS, there is one comment what is visible at the DevTools for some reason, although it is unactive. I mean " /* --colorName: Hue, Saturation, Lightness; */"
4. The hard part for me was that box-shadow for "Proceed to Payment" button. I don't know if I made it correct, although it looks similar to the picture.

Feel free to give me some feedback :) I don't know if I have write everything I had, maybe I forgot something so please feel free to ask me questions about that project and my solution so I try to answer to help you give me a more valuable feedback. I would be appreciate. And I apologize you for my poor English. Im trying hard to improve every day. I wish you good day :)

P.S. I have fixed all the bugs and problems. Although I am still waiting for more feedbacks. Thank you in advance :)