Canta is a flat Material Design theme for GTK 3, GTK 2 and Gnome-Shell which supports GTK 3 and GTK 2 based desktop environments like Gnome, Unity, Budgie, Pantheon, XFCE, Mate, etc.
This is not a theme issue, this is the default gnome-shell dash bar, dash to dock not disabled this, but dash to panel will disable this, so if you are using dash to panel, this will gone!
I am getting an extra side bar in the left side whenever I am opening the app desk.