If I press F4 on a symbol, the type hierarchy will pop up in the top right corner. When I am done using it, I have to manually click the X to close it. Is there a way to close it using a keyboard shortcut?
I didn't know this before, but your question prompted me to dig a bit, and I found that "F12" is a shortcut for "Activate Editor", which hides the Type Hierarchy view and gives focus back to the editor in your scenario.