This is a sample HTML/CSS/JavaScript that strictly follows our naming convention.
Reference for the guideline of CSS :
BEM
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For CSS class naming, we use [BEM](https://en.bem.info/) so that we can be sure that which rule will affect which part and also which rule will NOT affect any intended part.
Once tring BEM seriously in a complicated web site, we often face similar questions. Here are resources to answer such questions.