Bootstrap's collapsed menu should NOT open full-wdith

Bootstrap's collapsed menu should NOT open full-wdith

I want to get the following:
When a user opens the collapsed menu in Bootstrap it should NOT open
full-width, but with a max-width of 500px.
On codepen.io (http://codepen.io/cutterkom/pen/BdDAc) you can see, that
including .nav-collapse {max-width: 500px;} just stops the .active-class
at 500px (darker grey) but not the whole thing (lighter grey)
Do you have a clue, how to get it more narrow?
Best, cutterkom