Use blue arrows for blue admin's screen options and help tabs. Adjust baseline...

Use blue arrows for blue admin's screen options and help tabs. Adjust baseline to be more compatible with Firefox. props helenyhou. fixes #16114.



git-svn-id: https://core.svn.wordpress.org/trunk@20082 1a063a9b-81f0-0310-95a4-ce76da25c4cd