diff --git a/gtk/gtkentrycompletion.c b/gtk/gtkentrycompletion.c
index 05b965f2aa..9139109ebf 100644
--- a/gtk/gtkentrycompletion.c
+++ b/gtk/gtkentrycompletion.c
@@ -67,7 +67,6 @@
 
 #include "gtkintl.h"
 #include "gtkcellrenderertext.h"
-#include "gtkframe.h"
 #include "gtktreeselection.h"
 #include "gtktreeview.h"
 #include "gtkscrolledwindow.h"
@@ -464,7 +463,6 @@ gtk_entry_completion_constructed (GObject *object)
 {
   GtkEntryCompletion        *completion = GTK_ENTRY_COMPLETION (object);
   GtkTreeSelection          *sel;
-  GtkWidget                 *popup_frame;
   GtkEventController        *controller;
 
   G_OBJECT_CLASS (gtk_entry_completion_parent_class)->constructed (object);
@@ -526,14 +524,11 @@ gtk_entry_completion_constructed (GObject *object)
                             completion);
   gtk_widget_add_controller (completion->popup_window, controller);
 
-  popup_frame = gtk_frame_new (NULL);
-  gtk_popover_set_child (GTK_POPOVER (completion->popup_window), popup_frame);
-
   gtk_scrolled_window_set_child (GTK_SCROLLED_WINDOW (completion->scrolled_window),
                                  completion->tree_view);
   gtk_widget_set_hexpand (completion->scrolled_window, TRUE);
   gtk_widget_set_vexpand (completion->scrolled_window, TRUE);
-  gtk_frame_set_child (GTK_FRAME (popup_frame), completion->scrolled_window);
+  gtk_popover_set_child (GTK_POPOVER (completion->popup_window), completion->scrolled_window);
 }
 
 
diff --git a/gtk/gtkplacessidebar.c b/gtk/gtkplacessidebar.c
index 3995368478..eb49757eef 100644
--- a/gtk/gtkplacessidebar.c
+++ b/gtk/gtkplacessidebar.c
@@ -3774,7 +3774,6 @@ gtk_places_sidebar_init (GtkPlacesSidebar *sidebar)
   gtk_scrolled_window_set_policy (GTK_SCROLLED_WINDOW (sidebar->swin),
                                   GTK_POLICY_NEVER,
                                   GTK_POLICY_AUTOMATIC);
-  gtk_scrolled_window_set_has_frame (GTK_SCROLLED_WINDOW (sidebar->swin), TRUE);
 
   gtk_widget_add_css_class (GTK_WIDGET (sidebar), "sidebar");
 
diff --git a/gtk/gtkviewport.c b/gtk/gtkviewport.c
index 1348b2c5e0..412ba3b378 100644
--- a/gtk/gtkviewport.c
+++ b/gtk/gtkviewport.c
@@ -475,7 +475,6 @@ gtk_viewport_init (GtkViewport *viewport)
   viewport->hadjustment = NULL;
   viewport->vadjustment = NULL;
 
-  gtk_widget_add_css_class (widget, "frame");
   viewport_set_adjustment (viewport, GTK_ORIENTATION_HORIZONTAL, NULL);
   viewport_set_adjustment (viewport, GTK_ORIENTATION_VERTICAL, NULL);
 }
diff --git a/gtk/theme/Adwaita/_common.scss b/gtk/theme/Adwaita/_common.scss
index 0264c0bbbb..a4783877f1 100644
--- a/gtk/theme/Adwaita/_common.scss
+++ b/gtk/theme/Adwaita/_common.scss
@@ -3020,10 +3020,6 @@ actionbar > revealer >  box {
 }
 
 scrolledwindow {
-  > viewport.frame { // avoid double borders when viewport inside scrolled window
-    border-style: none;
-  }
-
   // This is used when content is touch-dragged past boundaries.
   // draws a box on top of the content, the size changes programmatically.
   > overshoot {
@@ -3407,8 +3403,6 @@ row image.sidebar-icon { opacity: $_placesidebar_icons_opacity; } // dim the sid
    https://gitlab.gnome.org/GNOME/gtk/-/issues/2929
 */
 placessidebar, .navigation-sidebar {
-  > scrolledwindow.frame { border-style: none; }
-
   list {
     padding: 4px 0;