Menu/nav when resizing browser doesn't work

Hey,

When I scale my browser right down so it’s quite narrow, the theme’s responsive feature is great, however the navigation/menu turns into a big grey button once it reaches a certain width, and it doesn’t work. You can click on it but nothing happens.

Can you help me?

http://www.justexplore.co.uk

Worried this is what people will see when viewing portrait on an iPad…

thanks

Laura

http://ww.wp.xz.cn/plugins/issuem/