Fix Topbar Size on Mobile

[William-McGonagle]

At the moment, on certain phones (including mine ☹️), the menu goes off the page and leads to some weird navigation. We just need to make the menu change size when it's on small screens.

If you're interested in helping with this, let me know.

Thank you!
Will

[Swetha-Baskaran]

@William-McGonagle I would like to help you with this.