svg buttons alignment on tabsbar

[jkup]

• 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).

Fix #5456

Auditors @bsclifton @luixxiul

Test Plan:

1. Open Brave
2. Create new tabs until you've filled up the tabs row
3. Make sure the + for the new tab button lines up with the kabob three dots for menu.
4. Three dots should be dark gray and turn black on hover.

Screenshots for @bradleyrichter's approval

and hover

[bsclifton]

Looks great, thanks! 😄