Hello Mehran,
Thank you for writing.
We have a great article on how to customize the page view in
BackStage Mode. Please have a look at it:
http://www.telerik.com/help/winforms/pageview-backstageview-customizing-backstageview.html
To change the particular properties, you may use the following code:
These will help you control the size, color, thickness, etc. of the line near the items, and also move the line to left or right, changing the width of the element in this way.
Hope this helps.
Regards,
Nikolay Aleksiev
the Telerik team