How to correctly set classes when layout for wordpress?

Question

css

Need help. I need to do a simple test work, but the difficulty is that I need to try to set the standard WordPress classes, but the template is not standard . Why am I asking for help - in real life I would go up to a wordpress and say "dude, I'm going to typeset this block, how will you display it and how can I make classes?" and he would have told me "dude, here's a link to the project for you, look at an identical block to yours." but this is a test work and besides you there’s no one to ask (.
I was given a link to the article, but I didn’t understand the WordPress kitchen at all + a non-standard template, and apart from pagination and the search output form, I don’t understand anything (.
I attach a slightly modified picture (whatever ...
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thank you very much