Please have a look at https://itunes.apple.com/us/app/koutoubia/id560563570?l=fr&ls=1&mt=8
I am interested by the bottom bar : it doesn't have the same height for all buttons, the selected button has a nice rounded hat. In the fourth screenshot, the rounded hat is ABOVE the main panel (zindex).
How would you that that with sencha ? A classic vbox won't do it. I believe that it is simply a matter of partially overlapping the toolbar and the main panel (so that the rounded hat is drawn on top of the main panel content).
I had a look at the relative/absolute positioning options for a sencha panel but I don't see how to use it for that specific example.