Hi Hyoung woo Lee,
I would suggest you set the Office_Blue theme as a custom application theme. Then find System.Windows.ScrollViewer.xaml and edit the scroll bar templates to your liking. This will automatically adjust the scroll bars of all our controls to look like you like.
NB! Do not edit the template of GridViewScrollViewer as it might affect grid's performance. Changing the scroll bars will affect the GridView control as well.
I have also prepared a sample to get you started. I hope you will find this useful.
the Telerik team