MC-3406: Explicit Background Attributes for Tab

 - stop overlay toggle for hidden blocks

Author: cspruiell

app/code/Magento/PageBuilder/view/adminhtml/web/css/source/content-type/block/_default.less

@@ -8,6 +8,9 @@
 //  _____________________________________________
 
 .pagebuilder-content-type .pagebuilder-block {
+    &:before {
+        content: '';
+    }
     .pagebuilder-block-placeholder {
         align-items: center;
         background-color: @color-gray98;
@@ -48,7 +51,7 @@
     }
 }
 
-.pagebuilder-content-type-hidden {
+:not(.pagebuilder-content-type-hidden) {
     > .pagebuilder-block.pagebuilder-content-type {
         &:before {
             content: '';

app/code/Magento/PageBuilder/view/adminhtml/web/js/content-type/block/preview.js

@@ -150,8 +150,5 @@ export default class Preview extends BasePreview {
      */
     private showBlockPreview(isShow: boolean) {
         this.displayingBlockPreview(isShow);
-
-        // preview is hidden only if block is shown
-        this.display(!isShow);
     }
 }