This is a page demo of Designed Theme
Navigation Stack can be added to any theme you have. Why?
Your theme might not have multi-dropdowns (like Designed) or be limited to 2 levels deep (like Split).
To add this automatic menu, you need to hide the current navigation with CSS. To do this will require some CSS skills. Use Safari Page Inspector to find the CSS class, hide the display and add the code to the page inspector CSS pane. For Designed theme the example code to get this effect would be:
.navbar-fixed nav {display: none;} #main {padding-top: 0;}