Update forms.less to add hover effect

[getsetbro]

• Submitted a ticket for my issue if one did not already exist.
• Used Github auto-closing keywords in the commit message.
• Added/updated tests for this change (for new code or code which already has tests).
• Ran git rebase -i to squash commits (if needed).

Test Plan:

Resolves issue #5953 "For the X, it should be @buttonColor when idle and #000 (black) when hovered."

[bsclifton]

Tested locally- looks great! 😄 Thanks!