getElementsByClassName with square brackets [closed]

I’m writing a simple search for elements on a page, and in one place I need to find an image reference that only has the class “sm:cap-h-[210px]”.

When writing such a request, for some reason I get the error “Uncaught SyntaxError: Unexpected token ‘[ ‘”.

document.getElementsByClassName('.sm:cap-h-[210px]').[0].src