I know of an option to hide the title bar, but I want to reduce height of title bar of tool windows such as "Output" or "Properties".
How can we change height of tool window's title bar in Visual Studio?
Actually, there is no such option or key to control the title height of a tool window in VS IDE.
Visual Studio does not allow to modify the title height of a tool window in VS IDE by default. And there is no such extensions to realize what you want.
Microsoft does not seem to open such interface. And what you want needs to inherit the VS built-in extension interface so that it can rewrite the title height of the tool window in VS IDE.
As a suggestion, you can suggest a feature on our User Voice Forum to reflect your requirements and I think Microsoft will consider your requirements carefully and give you a satisfactory feedback.
Hope it could help you.