make video responsive

transfersh-web/styles/includes/preview.less

@@ -86,6 +86,12 @@ padding: 20px;
   }
 }
 
-#md-preview {
+#md-preview,{
 	padding-bottom: 30px;
 }
+
+
+video {
+  margin: 0 auto;
+  width: 100%;
+}