align Mark all as done with other Done buttons on Todos page

What does this MR do?

Align "Mark all as done" with the other buttons. Also fixes inconsistent right margin for the "Mark All" and "Undo All" buttons

Are there points in the code the reviewer needs to double check?

not really

Why was this MR needed?

UI polish!

Screenshots (if relevant)

Before

After

Does this MR meet the acceptance criteria?

• Changelog entry added, if necessary
• [ ] Documentation created/updated
• [ ] API support added
• Tests
  • Added for this feature/bug
  • All builds are passing
• Conform by the merge request performance guides
• Conform by the style guides
• Branch has no merge conflicts with master (if it does - rebase it please)
• Squashed related commits together

What are the relevant issue numbers?

Closes #29555 (closed)