Need a vertical scroll bar in the left hand side predicate of press center page

Hi,

 I want to add vertical scroll bar in the left hand side predicate of press center page. I mean the press center page of geometrix site is having Tags section in the left hand side. Inside Tags we have Business, Architecrure and Building, Locations and Travel . I want to put the scroll bar for Business, Architecrure and Building, Locations and Travel so that i don't have to scroll down the whole page to see the subsequent options below it.

Please help me out in getting the scroll bar. I am not able to find the exact css class to modify it.

Regards,

prangya