content: fix font size for search header
content: fix font size for search header

Change-Id: I5c2f68074aacb2999d5afb8875a41271da1e8c27
Reviewed-on: https://team-review.git.corp.google.com/c/golang/discovery/+/505490
Reviewed-by: Robert Findley <9179eee875d1ee628c37fb47d7e749e855ffd21f@google.com>

golang/pkgsite,golang/pkgsite,golang/pkgsite,golang/pkgsite