Generalize and improve teaser styles.

services/web/public/stylesheets/app/editor.less

@@ -421,6 +421,7 @@
 	margin-bottom: 5px;
 }
 
+.teaser-video-container,
 .dropbox-teaser-video-container {
 	margin-top: -@modal-inner-padding;
 	margin-left: -@modal-inner-padding;
@@ -428,7 +429,10 @@
 	margin-bottom: 5px;
 	overflow: hidden;
 }
+
+.teaser-video,
 .dropbox-teaser-video {
 	width: 100%;
 	height: auto;
+	border-bottom: 1px solid @modal-header-border-color;
 }