Hide tab border for tab control

Check "Buttons" or "FlatButtons" for the Appearence property of the tab control. Or you could draw your own tab control by selecting "OwnerDrawFixed" for the DrawMode property

 

https://msdn.microsoft.com/en-us/library/system.windows.forms.tabcontrol.drawmode.aspx

 

http://www.dotnetspider.com/forum/313644-how-hide-tab-control-border-or-change-border.aspx

 

https://stackoverflow.com/questions/23247941/c-sharp-how-to-remove-tabcontrol-border