Twenty Fourteen: Ensure the content after the Read More tag is visible and has...

Twenty Fourteen: Ensure the content after the Read More tag is visible and has the appropriate padding.

Props ianbelanger, sabernhardt, slobodanmanic, Quantumstate, Gwendydd, andraganescu, francina.
Fixes #28967.
Built from https://develop.svn.wordpress.org/trunk@46429


git-svn-id: https://core.svn.wordpress.org/trunk@46227 1a063a9b-81f0-0310-95a4-ce76da25c4cd