[fix] force mat-header-cell invisible style

src/app/testing/color/color.testing.page.html

@@ -200,5 +200,8 @@
       </div>
     </section>
   </div>
+
+<!--  todo add divs with background colors-->
+
 </ion-content>
 

src/global.scss

@@ -501,6 +501,11 @@ ion-list {
       display: none;
     }
   }
+
+  // force invisible
+  &.cdk-visually-hidden {
+    position: absolute;
+  }
 }