fix content type editor property preview background in firefox

src/Umbraco.Web.UI.Client/src/less/components/umb-group-builder.less

@@ -279,6 +279,7 @@ input.umb-group-builder__group-sort-value {
   overflow: hidden;
   position: relative;
   padding: 35px 10px 25px 10px;
+  background: url("../img/checkered-background-20.png");
 }
 
 .umb-group-builder__property-preview:hover {
@@ -297,17 +298,6 @@ input.umb-group-builder__group-sort-value {
     display:none !important;
 }
 
-.umb-group-builder__property-preview-background {
-  position: absolute;
-  top: 0;
-  left: 0;
-  width: 100%;
-  height: 100%;
-  z-index: -1;
-  background: url("../img/checkered-background.png");
-  opacity: 0.2;
-}
-
 .umb-group-builder__property-preview-label {
   font-size: 11px;
   position: absolute;

src/Umbraco.Web.UI.Client/src/views/components/umb-groups-builder.html

@@ -232,8 +232,6 @@
                                     </umb-property-editor>
                                 </ng-form>
 
-                                <div class="umb-group-builder__property-preview-background"></div>
-
                             </div>
 
                             <!-- row tools -->