x/pkgsite: header blocks content unless screen is very wide

[3052]

What is the URL of the page with the issue?

https://pkg.go.dev/crypto/rand#Reader

What is your user agent?

Firefox

Screenshot

What did you do?

unless screen is quite wide, when you navigate to an item you cannot actually see the item, because the header is covering it - see example - I navigated to crypto/rand.Reader for example, did not scroll at all, yet the entry is not visible as the header is covering it

What did you see happen?

!

What did you expect to see?

ideally just stop making the header sticky - people have a HOME key that moves to the top instantly, so maintaining a buggy header is dubious

[cagedmantis]

cc @golang/pkgsite