[x/go.dev] all: use relative path for CSS link
[x/go.dev] all: use relative path for CSS link

The Permalink resource point uses the baseURL, when a relative path is
fine. Fixes CSS issue on staging.
X-GoDev-Commit: a097c8e80ec08aaa9e265b5b03824b12ee61c80a

golang/website,golang/website,golang/website,golang/website,golang/website,golang/website,golang/website