Customize: Maximize height of Custom CSS textarea without causing doubled scrollbars.

Textarea will fill vertical height of Custom CSS section for browsers that support `calc()` and when plugins don't add other controls to the section. Also run CSS autoprefixer.

Props michaelarestad, westonruter.
See #35395.
Fixes #38755.

Built from https://develop.svn.wordpress.org/trunk@39229


git-svn-id: http://core.svn.wordpress.org/trunk@39169 1a063a9b-81f0-0310-95a4-ce76da25c4cd

wp-includes/css/customize-preview-rtl.css

@@ -55,6 +55,8 @@
 	box-shadow: 0 2px 1px rgba(46,68,83,0.15);
 	text-align: center;
 	cursor: pointer;
+	-webkit-box-sizing: border-box;
+	-moz-box-sizing: border-box;
 	box-sizing: border-box;
 	padding: 3px;
 	-webkit-animation-fill-mode: both;
@@ -86,6 +88,7 @@
 }
 
 .customize-partial-edit-shortcut button:focus {
+	-webkit-box-shadow: 0 0 0 2px #008ec2;
 	box-shadow: 0 0 0 2px #008ec2;
 }