Refactor the custom css file using SASS feature Nesting & Variables

Change-Id: I22adcaffbd29db0fb06074aed929b1180c25b68d
Further refactor customer css file using variables defined by Bootstrap (http://bootstrapdocs.com/v2.0.4/docs/less.html)

Change-Id: I9ea025cc25218d758ff6fe5223bc3238f0a86677