For accessibility reasons it is considered good practice to put a ”skip navigation” link at the top of each page (In this case, ”top” means first or very early on in the HTML document, not necessarily the same thing as being displayed at the top of the page in a graphical browser.), allowing users to jump directly to the main content of the page.
To hide this link from graphical web browsers a widely used method has been to use
display:none. The problem is that this will also hide it from some screen readers, which makes the link pretty useless.