Pages become slightly smaller when they get the selected border

This issue has been migrated from mozilla/webmaker-android#1835.

It was originally written by flukeout on Tue May 12 2015 and had the following description:

Let's make all pages appear the same size.

On Tue May 12 2015, thisandagain commented:

Tried resolving this by moving the border from the selected class to the base class for each page, but it caused major performance problems. Not sure why ... needs investigation but any potential fix for this should be tested for perf.