Rename class name in placeholder

applies 2535e060a48393143e7a6c2eb93a0a5d06663801 to css.html. Wasn't
docs.html removed a while ago?
Remove the offcanvas js from the footer

This was moved inline in 65ad52060e1f9b5928ac0d5a0bfead0cdf1b26f4
Merge pull request #8251 from acmetech/3.0.0-wip

Remove offcanvas from footer and change placeholder in css.html