title: Remove shadow from XFCE panel
body: <p>I am new in GTK theming. Now I am trying to create theme GTK for XFCE. Everything is OK but how to remove this ugly shadow under the panel?
  <a href="https://i.stack.imgur.com/ydviz.png" rel="nofollow noreferrer"><img src="https://i.stack.imgur.com/ydviz.png" alt="XFCE panel and thunar in fullscreen mode"></a></p>