diff --git a/gtk/theme/HighContrast/_common.scss b/gtk/theme/HighContrast/_common.scss
index 63fe601489..13afba9bbb 100644
--- a/gtk/theme/HighContrast/_common.scss
+++ b/gtk/theme/HighContrast/_common.scss
@@ -2618,6 +2618,7 @@ row.activatable {
                               mix(black, $bg_color, 4%));
   // FIXME no space for outer shadow : box-shadow: 0 1px 1px rgba(0,0,0,.5);
   .button { padding: 6px; }
+  border { border-width: 0; }
 }
 
 /*************
diff --git a/gtk/theme/HighContrast/gtk-contained-inverse.css b/gtk/theme/HighContrast/gtk-contained-inverse.css
index 65db2ef76c..2ceb61eeab 100644
--- a/gtk/theme/HighContrast/gtk-contained-inverse.css
+++ b/gtk/theme/HighContrast/gtk-contained-inverse.css
@@ -2767,6 +2767,9 @@ row.activatable {
   .app-notification .button,
   .app-notification.frame .button {
     padding: 6px; }
+  .app-notification border,
+  .app-notification.frame border {
+    border-width: 0; }
 
 /*************
  * Expanders *
diff --git a/gtk/theme/HighContrast/gtk-contained.css b/gtk/theme/HighContrast/gtk-contained.css
index b349f778ab..994d5637d4 100644
--- a/gtk/theme/HighContrast/gtk-contained.css
+++ b/gtk/theme/HighContrast/gtk-contained.css
@@ -2774,6 +2774,9 @@ row.activatable {
   .app-notification .button,
   .app-notification.frame .button {
     padding: 6px; }
+  .app-notification border,
+  .app-notification.frame border {
+    border-width: 0; }
 
 /*************
  * Expanders *