Click on the three lines (☰) in the Employees region title. The sidebar will open or close.

The sidebar will remember it's open or closed state when you navigate away from the page. The open or closed state is stored in an APEX User Preference.
Note that this preference is user specific, if you're not logged in, the value is shared with anyone looking at the demo
For more information about this page, check out these blog posts:

• http://rimblas.com/blog/2014/04/enhancing-the-menu-drawer-using-preferences
• http://rimblas.com/blog/2014/04/building-a-menu-drawer-in-your-apex-desktop-app/