Make email preview responsive

Make email preview responsive

Author: BrentRobert

app/design/adminhtml/Magento/backend/web/css/styles-old.less

@@ -4070,6 +4070,21 @@
     }
 }
 
+.adminhtml-email_template-preview {
+    .cms-revision-preview {
+        padding-top: 56.25%;
+        position: relative;
+
+        #preview_iframe {
+            height: 100%;
+            left: 0;
+            position: absolute;
+            top: 0;
+            width: 100%;
+        }
+    }
+}
+
 .admin__scope-old {
     .buttons-set {
         margin: 0 0 15px;