diff --git a/banner.js b/banner.js
index a24dbdd..836395f 100644
--- a/banner.js
+++ b/banner.js
@@ -147,7 +147,10 @@
 
     // The button was sized (min-width, padding) to fit the icon + label
     // together; with the label gone, shrink it to fit just the icon instead
-    // of leaving the label's dead space behind.
+    // of leaving the label's dead space behind. It's a flex item in the
+    // toolbar, so flex-grow/flex-basis would otherwise override the explicit
+    // width below and keep reserving the old footprint.
+    container.style.setProperty('flex', '0 0 auto', 'important');
     container.style.setProperty('min-width', '0', 'important');
     container.style.setProperty('width', 'fit-content', 'important');
   }