diff --git a/gtk/theme/Adwaita/gtk-contained-dark.css b/gtk/theme/Adwaita/gtk-contained-dark.css
index da5c453d40..5f68aec247 100644
--- a/gtk/theme/Adwaita/gtk-contained-dark.css
+++ b/gtk/theme/Adwaita/gtk-contained-dark.css
@@ -3789,7 +3789,7 @@ frame > border,
   padding: 0;
   border-radius: 0;
   border: 1px solid #1b1f20; }
-  frame > border.flat,
+  frame.flat > border,
   .frame.flat {
     border-style: none; }
   frame > border:backdrop,
diff --git a/gtk/theme/Adwaita/gtk-contained.css b/gtk/theme/Adwaita/gtk-contained.css
index c0f43698d0..7830a16779 100644
--- a/gtk/theme/Adwaita/gtk-contained.css
+++ b/gtk/theme/Adwaita/gtk-contained.css
@@ -3820,7 +3820,7 @@ frame > border,
   padding: 0;
   border-radius: 0;
   border: 1px solid #b6b6b3; }
-  frame > border.flat,
+  frame.flat > border,
   .frame.flat {
     border-style: none; }
   frame > border:backdrop,
diff --git a/gtk/theme/HighContrast/gtk-contained-inverse.css b/gtk/theme/HighContrast/gtk-contained-inverse.css
index da9ab5bc24..0a6dea1564 100644
--- a/gtk/theme/HighContrast/gtk-contained-inverse.css
+++ b/gtk/theme/HighContrast/gtk-contained-inverse.css
@@ -2616,7 +2616,7 @@ frame border,
 .frame {
   border: 1px solid gray;
   padding: 0; }
-  frame border.flat,
+  frame.flat > border,
   .frame.flat {
     border-style: none; }
   frame border:backdrop,
diff --git a/gtk/theme/HighContrast/gtk-contained.css b/gtk/theme/HighContrast/gtk-contained.css
index 045cc08885..8adbd5a957 100644
--- a/gtk/theme/HighContrast/gtk-contained.css
+++ b/gtk/theme/HighContrast/gtk-contained.css
@@ -2623,7 +2623,7 @@ frame border,
 .frame {
   border: 1px solid gray;
   padding: 0; }
-  frame border.flat,
+  frame.flat > border,
   .frame.flat {
     border-style: none; }
   frame border:backdrop,