How to apply a class to all nested pages?

Question

1C-Bitrix

Good afternoon! Tell me how to apply the class to all pages of the section. That's what we have now, but this method only applies to a specific page.

Answer 1

Tell me how to apply the class to all pages of the section.

1) Have you opened the pages before? Those. Are previous pages cached? Have you tried clearing the cache?
2) How exactly do you connect your style? Through inline, file connection or some other way?
3) Do you apply to pages of the same type? Or to different ones?