There are 0 results on SO for CssHierarchyControl and 3 irrelevant results on Google for CssHierarchyControl C#.
What is this control? How does it differ from a ComboBox?
From the tooltips from hovering on each of the controls: ComboBox is at v4.5.0.0, whereas CssHierarchyControl states v11.0.0.0.

The
CssHierachyControlis on my machine as well. Looking under the “Choose Items” context menu on the toolbox I see it listed as part of theMicrosoft.TeamFoundation.Clientnamespace in theMicrosoft.TeamFoundation.Clientassembly. It is version 11.0.0.0 as well, which matches the version number of Visual Studio 2012, which is 11.Looking at the class in dotPeek it does inherit from
System.Windows.Forms.ComboBoxso it is a combo box.It is not listed as part of the Microsoft.TeamFoundation.Client namespace so it is not meant for public consumption so you should remove it from your tools list since there is no reason to ever use it.