Tightening up popover arrow css scope to apply only to direct descendant arrows.
Remove comma first rule

Removes outdated coding style rule.
Add examples/**/*css in the csslint task.

Fixes #12457.
Examples: fix csslint errors.
fix #12494 in the migration docs
Merge pull request #12533 from 1000hz/tighten-popover-arrows-scope

Scope popover arrow css to direct descendant
Merge pull request #12553 from ZDroid/nocf

Remove comma first rule
Don't offset customizer alert, grunt dist
Merge pull request #12466 from XhmikosR/12457

Add examples/css in the csslint task.