Twenty Sixteen: Makes sure quote block plain style is in editor.

The plain style for quote block was not showing in the editor despite showing on the front. This patch now makes sure it also does not show the border in editor.

Reviewed by audrasjb, karmatosed.
Merges [60342] to the 6.8 branch.
Props nidhidhandhukiya, dilipbheda, sabernhardt, sainathpoojary, dhruvang21, harshgajipara, SirLouen, darshitrajyaguru97, jorbin.
Fixes #63424.



git-svn-id: https://develop.svn.wordpress.org/branches/6.8@60426 602fd350-edb4-49c9-b593-d223f7449a82

Author: audrasjb

src/wp-content/themes/twentysixteen/css/editor-blocks.css

@@ -370,6 +370,10 @@ figure[class*="wp-block-"] > figcaption {
 	padding-right: 0;
 }
 
+.wp-block-quote.is-style-plain {
+	border: none;
+}
+
 @media screen and (min-width: 44.375em) {
 	.wp-block-quote.alignleft,
 	.wp-block-quote.alignright {