[x/go.dev] footer: add underline to parent menu items
[x/go.dev] footer: add underline to parent menu items

Change-Id: I8be1f6464d2daf41a49e4f85572a18280d39fcfd

X-GoDev-Commit: 1b03acc72b7e58c1983ca07f6d5bdaedeb153a03

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