custom page layout the easiest way

Hello!

I would like to ask, what is the best and easiest way to make custom page layout like these:

https://www.brownthomas.com/living

https://www.brownthomas.com/beauty/beauty-news/chanel-inimitable-intense-mascara

I would need to use it as template, because not all of the posts or pages need to be like these.

I am not experienced with theme customization, so it would be great if someone could suggest a solution with code digging…

I have html and css knowledge, so if there is no other option, is it possible to code it in html, and if I do so, please give me some tips for what I have to pay attention.

Thank You very much for Your help!