How to format the nav menu button on tablet

Site URL: https://www.cdfielddays.co.nz/

Hi there,

I can't seem to figure out how to format my nav menu button for tablet/smaller screen view. When the window on a computer is made smaller or viewed on a tablet, it formats the button onto two lines and it makes the nav menu very deep - is there any way to make the button automatically resize depedning on what screen size it is viewed on?

Have got it working on mobile all ok. Screenshot of smaller screen view attached.

Thank you!