Hideaway – Offscreen/Toggle Menu
The Hideaway theme features a custom, offscreen/toggle menu that is displayed in the top right corner of your header. When the menu icon is clicked, the contents of the offscreen menu area will appear.
Offscreen menu when closed:

Offscreen menu when open:

Setting up the offscreen menu
The content inside of the offscreen menu is housed in a custom widget area, which can be found at Appearance > Widgets > Offscreen Menu
As long as you imported the demo content, the offscreen menu should be fully set up for you already!
How to adjust the menu, social icons, and other content inside of the offscreen menu: