I am accessing a mac using screen sharing. 

If I try to take a screenshot of a window using the built-in screenshot tool, I find that the screenshot consists of white background with shadow border as below.[![enter image description here][1]][1]

Can anyone point out how to take screenshot while using screen sharing?

Edit-

- The mac that is accessing through screen sharing is running macOS Mojave (10.14.6)
- I am using TigerVNC client software running on Linux to access the mac.


  [1]: https://i.sstatic.net/enLJt.png