Unzip “vBulletin_3_fBLight” and upload to cpstyles (site.com/forum/cpstyles/)
Log into your Admin control panel.
vBulletin Options.
Admin Control Panel Options.
Set it to ‘vBulletin_3_fBLight’.
Notes
Dark Style: http://www.vbulletin.org/forum/showthread.php?t=103461