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

Props iamtakashi, fixes #30521.



Built from https://develop.svn.wordpress.org/trunk@30588


git-svn-id: http://core.svn.wordpress.org/trunk@30578 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: overflow hidden can hide focus outlines here so out it goes.

Props iamtakashi, fixes #30523.


Built from https://develop.svn.wordpress.org/trunk@30589


git-svn-id: http://core.svn.wordpress.org/trunk@30579 1a063a9b-81f0-0310-95a4-ce76da25c4cd
Twenty Fifteen: better highlights for tapped links in iOS Safari.

Props iamtakashi, fixes #30524.



Built from https://develop.svn.wordpress.org/trunk@30590


git-svn-id: http://core.svn.wordpress.org/trunk@30580 1a063a9b-81f0-0310-95a4-ce76da25c4cd