Best practices for HTML, CSS and almost any language 🤨

For me the best practice is to use semantic HTML tags.
There are several examples and I don't want to decide, which works the best for you. It will depends on the project.
As mentioned before me, you can use semantic HTML tags.
I always use 1 <nav> tag at the top level which contains all my navigation links at the top of my page. 1 <main> tag that contains all my content which is related to my page and 1 <footer>.
My advise is don't overuse <div>.It will helping you to make better SEO (and user) experience. Look at HTML as a skeleton for your page. I know it could be overwhelming at first.
You can read more about it here:
https://www.w3schools.com/html/html5_semantic_elements.asp

For CSS there are multiple best practices. BEM also mentioned here which could help you to keep all your CSS files DRY. For me, I'm using SCSS 7-1 (sometimes 7-2) patterns, but it is really up to you (and the project), which works the best for you.
BEM is a naming convention for CSS classes. (BEM stands for Block Element Modifier).
You can read more about BEM here: https://css-tricks.com/bem-101/
and about 7-1 sass architecture: https://www.learnhowtoprogram.com/user-interfaces/building-layouts-preprocessors/7-1-sass-architecture

As I said HTML is the skeleton for your page, CSS is the muscles, skin and hair.

Hope it will help!