which part do you mean? there is no dynamic require but there is resolve. can't have dynamic require outside the REPL or a self-hosted build though.

It's just a part of the class name, btn--link.

so it could be btn.link also ?

Well, that would be two classes then, btn and link. If you need to have a dot as a part of a class name, you can't use that shorthand - instead, you'd use the :class property.

Or if you mean that you can write btn.link instead of btn.btn--link - well, if you're the author of the relevant CSS and if you don't have any DOM queries that rely on btn--link, then sure. But it would also have to be a very careful decision from a design standpoint. btn--link is very clearly for a button whereas link is who knows for what. Given that you can mix multiple CSS classes, going with plain link might make some things much harder.

there are several naming patterns for CSS. this looks like BEM, see http://getbem.com/naming/

Most likely, you're using Reagent. The symbol itself is nothing special in CLJS, but Reagent treats it as a special component where the second argument is a native component. Documented somewhere in the Reagent's repo.

thank you

here: https://cljdoc.org/d/reagent/reagent/1.1.1/doc/tutorials/interop-with-react