no-bug: Make sure to flush the document styles when showing essentials promo (gh-12908)

src/browser/themes/shared/zen-icons/icons.css

@@ -84,7 +84,8 @@
   max-height: 16px;
 }
 
-#appMenu-translate-button {
+#appMenu-translate-button,
+#translations-button-icon {
   list-style-image: url("translations.svg") !important;
 }
 

src/zen/tabs/ZenEssentialsPromo.mjs

@@ -61,6 +61,8 @@ export function createZenEssentialsPromo(container = undefined) {
   const element = document.createXULElement(TAG_NAME);
   section.appendChild(element);
   section.essentialsPromo = element;
+  // Trigger re-calculation of pinned height to avoid any flickering
+  void section.offsetHeight;
   updatePinnedHeight();
   return "created";
 }