I applied some updates for Ubuntu 16.04 today, restarted and now some widgets are shown in a ugly default theme instead of the standard Ambient theme. Most widgets are displayed correctly (Gnome-terminal seems to be normal, for example)
For example, the tabs or the popups in Chrome are looking strange.
How do I exactly find out, what's causing this problem?
Ubuntu 16.04, mostly out-of-the-box-configuration. Using NVIDIA binary driver, version 367.57 on a Quadro K1100M (this is a hybrid-thingy, using just the Intel GPU)