How to choose a name for variables, classes and Id for layout elements?

Question

PHP

Hello, I have a problem, how many years I have been writing and typesetting, all the time I am faced with the difficulty of correctly determining the name for a variable or id for html, in the case of the code there is nothing, everything can be divided into local functions and use a specific set, directly by meaning. But, if we talk about layout, naming css classes is just hell.
How to do it correctly (choose a name for the class and id css), so as not to get confused later?

Answer 1

1) don't use ID
2) BEM
3) Css Modules