Fix expanded search button in sidebar

At the moment when expanding the seachbox in the sidebar, the secondary search button (underneath "limit my search" has no right border, and has the search icon and "Search" text overlapping. 

Added "color: transparent;" to hide the "Search" text
Removed "border-right: 0px solid;" to implement a right border on the search button (via "border: 1px solid #D5D5D5;")