Button and progress bar style improvements

- The buttons in the main notebook (ICC Profile Creator, Preferences,
Fullscreen) and the buttons in the bottom-left corner under the preview
(Save, Sent to queue, Send to GIMP) are now consistently flat to match
all other toolbar buttons.
- Progress bar thicker and more centered in their containers.

rtdata/themes/RawTherapee-GTK3-20_.css

@@ -368,29 +368,7 @@ separator {
     margin: 5px;
 }
 
-progressbar.vertical trough {
-    min-width: 6px;
-}
-progressbar.vertical trough progress {
-    min-width: 6px;
-}
-
-progressbar.horizontal trough {
-    min-height: 6px;
-}
-progressbar.horizontal trough progress {
-    min-height: 6px;
-}
-
-progressbar trough {
-    background-color: #2A2A2A;
-    border-color: #202020;
-}
-
-notebook header progressbar trough {
-    background-color: #202020;
-    border-color: #181818;
-}
+/* */
 
 .drawingarea {
     border-radius: 0;
@@ -1016,3 +994,36 @@ button.combo, .image-combo .toggle, #MyFileChooserButton {
     padding-right: 4px;
 }
 
+
+/* Progress bars */
+
+progressbar.horizontal {
+    min-width: 100px;
+    margin-bottom: 4px;
+}
+
+progressbar.vertical {
+    min-height: 100px;
+/*    margin: 8px 8px 8px 0;*/
+}
+
+progressbar trough {
+    background-color: #383838;
+    border: none;
+}
+
+progressbar progress {
+    border-color: #363636;
+    background-color: #FFCC00;
+    background-color: #215d9c;
+}
+
+progressbar.horizontal trough, progressbar.horizontal progress {
+    min-height: 8px;
+}
+
+progressbar.vertical trough, progressbar.vertical progress {
+    min-width: 8px;
+}
+
+/* */