diff --git a/themes/Default/common-light.css b/themes/Default/common-light.css
index a16892d011..a3110a2d04 100644
--- a/themes/Default/common-light.css
+++ b/themes/Default/common-light.css
@@ -30,3 +30,12 @@ paned.vertical > separator {
 button:not(.flat) {
   box-shadow: 0 1px @extreme-bg-color inset;
 }
+
+/* Define GimpSpinScale slider colors */
+GimpSpinScale entry {
+  background-color: @extreme-bg-color;
+}
+
+GimpSpinScale entry progress {
+  background-color: @widget-bg-color;
+}
diff --git a/themes/Default/common.css b/themes/Default/common.css
index af3d7b2c72..0eadfd7080 100644
--- a/themes/Default/common.css
+++ b/themes/Default/common.css
@@ -436,6 +436,7 @@ spinbutton
 {
   background-image: none;
   background-color: @bg-color;
+  box-shadow:       none;
 }
 
 /* Styling for the +/- buttons */
@@ -444,16 +445,38 @@ spinbutton button.up, spinbutton button.down {
   -gtk-icon-shadow: none;
 }
 
-GimpSpinScale entry progress {
-  background-color: @extreme-selected-color;
-  border-width:     0px;
-  border-radius:    3px;
+GimpSpinScale {
+  border-radius: 6px;
+  box-shadow:    0px 0.5px @stronger-border-color;
 }
 
-GimpSpinScale button
-{
-  border-color: @border-color;
+GimpSpinScale entry {
+  padding:            0px 8px 0px 5px;
+  background-color:   @stronger-border-color;
+  border-color:       @edge-border-color;
+  border-radius:      5px 0px 0px 5px;
+  border-right-width: 0px;
+  box-shadow:         none;
+}
+
+GimpSpinScale entry progress {
+  background-color: @extreme-bg-color;
+  border-width:     0px;
+  border-radius:    3px 0px 0px 3px;
+  margin:           0px -8px 0px -5px;
+}
+
+GimpSpinScale button {
   -gtk-icon-shadow: none;
+  border-color:     @border-color;
+  border-radius:    0px 0px 0px 0px;
+  box-shadow:       0px 0.5px @stronger-border-color;
+}
+
+/* Round the right-side edge of the end button */
+GimpSpinScale button:nth-child(odd) {
+  border-left-width: 0px;
+  border-radius:     0px 5px 5px 0px;
 }
 
 /* Checkboxes */