diff --git a/gtk-3.0/gtk-widgets.css b/gtk-3.0/gtk-widgets.css
index 283a7d0..a64d06d 100644
--- a/gtk-3.0/gtk-widgets.css
+++ b/gtk-3.0/gtk-widgets.css
@@ -299,6 +299,13 @@ GtkAssistant .sidebar {
     background-color: shade(@theme_selected_bg_color, 0.97);
 }
 
+.button.flat,
+.button.flat:insensitive {
+    border-color: transparent;
+    background-color: transparent;
+    background-image: none;
+}
+
 /****************
  * cell and row *
  ****************/
@@ -2409,6 +2416,23 @@ GtkColorButton.button {
     color: @toolbar_fg_color;
 }
 
+.primary-toolbar GtkComboBox.flat,
+.primary-toolbar .button.flat,
+.primary-toolbar GtkComboBox.flat,
+.primary-toolbar .button.flat,
+.toolbar GtkComboBox.flat,
+.toolbar .button.flat,
+.primary-toolbar GtkComboBox.flat:insensitive,
+.primary-toolbar .button.flat:insensitive,
+.primary-toolbar GtkComboBox.flat:insensitive,
+.primary-toolbar .button.flat:insensitive,
+.toolbar GtkComboBox.flat:insensitive,
+.toolbar .button.flat:insensitive {
+    border-color: transparent;
+    background-color: transparent;
+    background-image: none;
+}
+
 .primary-toolbar .raised .button,
 .primary-toolbar .raised.button,
 .toolbar GtkComboBox,