The problem: you click a jump link like
<a href="#header-3">Jump</a> which links to something like
<h3 id="header-3">Header</h3>. That’s totally fine, until you have a
position: fixed; header at the top of the page obscuring the header you’re trying to link to!
Fixed headers have a nasty habit of hiding the element you’re trying to link to. … Read article “Fixed Headers and Jump Links? The Solution is scroll-margin-top”