Twenty Fifteen: minor corrections to borders and post title colors in custom color schemes.

Props iamtakashi, fixes #30521.




git-svn-id: https://develop.svn.wordpress.org/trunk@30588 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: overflow hidden can hide focus outlines here so out it goes.

Props iamtakashi, fixes #30523.



git-svn-id: https://develop.svn.wordpress.org/trunk@30589 602fd350-edb4-49c9-b593-d223f7449a82
Twenty Fifteen: better highlights for tapped links in iOS Safari.

Props iamtakashi, fixes #30524.




git-svn-id: https://develop.svn.wordpress.org/trunk@30590 602fd350-edb4-49c9-b593-d223f7449a82