Adding Collapsible menu in nav bar


Hello All,
I want to add an option like this.

On which when i click, this should open

But at ghost i added

I had put styling in default.hbs and html part in site-nav.hbs.
But when i hover or click it, it changes the colour but menu does not open up.

And when i tried collapsible bootstrap


And when i click it then.

Please help me out.