diff --git a/rtdata/themes/rtcommon.css b/rtdata/themes/rtcommon.css
index 6c9b3b179..f56c999c4 100644
--- a/rtdata/themes/rtcommon.css
+++ b/rtdata/themes/rtcommon.css
@@ -20,6 +20,7 @@
  Please keep this gtkrc in sync with the other ones from Clearlooks based themes.
 */
 
+/* Declared for reference, they're actually unused */
 @define-color rt_salt_pinch        #95B0DB;
 @define-color rt_base_color        #dddddd;
 @define-color rt_fg_color          #0A0A0A;
@@ -36,6 +37,10 @@ GtkLabel, GtkComboBox, GtkEntry, GtkDrawingArea, GtkTreeView, GtkListTree {
 	color: #AAAAAA;
 }
 
+GtkButton, GtkCheckButton, GtkLabel {
+	padding: 0px;
+}
+
 GtkFrame > GtkLabel {
 	color: #EEEEEE;
 }
@@ -80,21 +85,25 @@ GtkFrame {
 	background-color: rgba(128,128,128,0.15);
 }
 
-GtkNotebook tab GtkLabel,
-GtkNotebook tab GtkImage {
-	margin: 2px;
+GtkNotebook {
+	padding: 4px;
+}
+
+GtkNotebook tab GtkLabel {
 	padding: 4px;
 	font-size: 120%;
 	font-weight: bold;
 }
 
-GtkNotebook {
-	padding: 5px;
+GtkNotebook tab GtkButton {
+	padding: 2px;
+}
+
+GtkNotebook tab GtkImage {
+	padding: 2px;
 }
 
 GtkButton {
-	margin: 2px;
-	padding: 2px;
 	border-style: solid;
 	border-width: 1px;
 	border-radius: 4px;
@@ -144,13 +153,8 @@ GtkButton.Right {
 }
 
 GtkEntry, GtkSpinButton {
-	padding: 2px;
-	margin: 2px;
-}
-
-
-GtkNotebook tab GtkButton, GtkNotebook tab GtkImage {
 	padding: 1px;
+	margin: 1px;
 }
 
 GtkMenu {
diff --git a/rtdata/themes/slim.css b/rtdata/themes/slim.css
index 6a878976e..256655bf7 100644
--- a/rtdata/themes/slim.css
+++ b/rtdata/themes/slim.css
@@ -17,7 +17,30 @@
   along with RawTherapee.  If not, see <http://www.gnu.org/licenses/>.
 */
 
-* {
-	padding: 1px;
-	margin: 1px;
+ProgressBar {
+	padding: 2px;
+}
+
+GtkNotebook {
+	padding: 2px;
+}
+
+GtkNotebook tab GtkLabel {
+	padding: 2px;
+}
+
+GtkNotebook tab GtkButton {
+	padding: 1px;
+}
+
+GtkNotebook tab GtkImage {
+	padding: 1px;
+}
+
+GtkImage {
+	padding: 1px;
+}
+
+.BIG {
+	padding: 4pt;
 }
diff --git a/rtgui/guiutils.cc b/rtgui/guiutils.cc
index d8574b5f9..a7a7771d7 100644
--- a/rtgui/guiutils.cc
+++ b/rtgui/guiutils.cc
@@ -533,7 +533,7 @@ void ExpanderBox::setLevel(int level)
 
 void ExpanderBox::updateStyle()
 {
-    set_border_width(options.slimUI ? 2 : 8);  // Outer space around the tool's frame 2:7
+    set_border_width(options.slimUI ? 2 : 7);
 }
 
 void ExpanderBox::show_all()
diff --git a/rtgui/preferences.cc b/rtgui/preferences.cc
index 2e377c974..eee49c079 100644
--- a/rtgui/preferences.cc
+++ b/rtgui/preferences.cc
@@ -1953,7 +1953,9 @@ void Preferences::fontChanged ()
 void Preferences::switchThemeTo(Glib::ustring newTheme, bool slimInterface)
 {
 
-    Glib::ustring filename(argv0 + "/themes/" + options.theme + ".css");
+    //Glib::ustring filename(argv0 + "/themes/" + options.theme + ".css");
+    // Forcing the default dark theme
+    Glib::ustring filename(argv0 + "/themes/rtcommon.css");
 
     if (!css) {
         css = Gtk::CssProvider::create();
@@ -1970,14 +1972,20 @@ void Preferences::switchThemeTo(Glib::ustring newTheme, bool slimInterface)
     options.slimUI = slimInterface;
 
     if (slimInterface) {
+        bool slimCreated = false;
         if (!cssSlim) {
             cssSlim = Gtk::CssProvider::create();
+            slimCreated = true;
         }
 
         filename = argv0 + "/themes/slim.css";
 
         try {
             cssSlim->load_from_path (filename);
+            if (slimCreated) {
+                Glib::RefPtr<Gdk::Screen> screen = Gdk::Screen::get_default();
+                Gtk::StyleContext::add_provider_for_screen(screen, cssSlim, GTK_STYLE_PROVIDER_PRIORITY_APPLICATION);
+            }
         } catch (Glib::Error &err) {
             printf("Error: Can't load css file \"%s\"\nMessage: %s\n", filename.c_str(), err.what().c_str());
         } catch (...) {
diff --git a/rtgui/toolpanel.cc b/rtgui/toolpanel.cc
index 4a863604f..80d75f1a1 100644
--- a/rtgui/toolpanel.cc
+++ b/rtgui/toolpanel.cc
@@ -55,8 +55,8 @@ void ToolParamBlock::updateStyle()
         set_spacing(2);       // Vertical space between parameters in a single tool
         set_border_width(6);  // Space separating the parameters of a tool and its surrounding frame  6
     } else {
-        set_spacing(4);       // Vertical space between parameters in a single tool
-        set_border_width(8);  // Space separating the parameters of a tool and its surrounding frame  8
+        set_spacing(2);       // Vertical space between parameters in a single tool
+        set_border_width(7);  // Space separating the parameters of a tool and its surrounding frame  8
     }
 }