Drop-down menu and Join page

The drop-down colour has suddenly changed to the same as the background of the drop-down so we cannot see the text. How can I change the drop-down background as I want to keep the same text colour? (I’m not a code editing type).

The second issues is that the Join page has disappeared. There is a heading in the menu but it does not go anywhere and I cannot see the page in the dashboard.

https://hendersonlincolnbusiness.co.nz/

Thanks