I have a question about the first paragraph of the task, which is:
quote - You can use CSS to make elements with this class completely hidden from the visual page, but still be announced by screen readers. - unquote.
Why would I want to keep something visually hidden but be announced by screen readers?
Maybe you have an image or a graphic for the sighted users, but to convey that same information to visually impaired users, you need text, which instead you may want to hide from the sighted users
Welcome to the forum!
A use case for this would be instructions or descriptions for visually impaired or blind users.