Yeah, that +
is an Adjacent sibling combinator:
https://developer.mozilla.org/en-US/docs/Web/CSS/Adjacent_sibling_combinator
Its about one of the very few ( kinda ) logic operators with CSS.
More on combinators:
https://developer.mozilla.org/en-US/docs/Learn/CSS/Building_blocks/Selectors/Combinators
glad to hear thats working for you 🙂