Change mobile menu to drop down

Hello everyone!

I have just moved to the free Catch Box theme, which I love. I’ve managed to customise it to how I want it except for one thing… the main menu when in mobile screen size. It currently uses a normal dropdown but I’d much prefer a fixed dropdown menu using one of those three ||| (horizontal) line buttons.

I don’t suppose anyone knows some easy code to create that?

This is my site at the moment LoveClapham.com

Thanks,

Jack