Use tabPadding property in Windows theme

themes/chrome/main.css

@@ -126,6 +126,11 @@ ToolButton[toolbar-look="true"]:pressed
 }
 
 /*TabWidget*/
+#tabbar
+{
+    qproperty-tabPadding: -1;
+}
+
 #tabbar::scroller
 {
     width: 0px;

themes/linux/main.css

@@ -67,6 +67,11 @@
 }
 
 /*TabWidget*/
+#tabbar
+{
+    qproperty-tabPadding: -1;
+}
+
 #tabbar-button-right
 {
     qproperty-themeIcon: "arrow-right";

themes/mac/main.css

@@ -127,6 +127,11 @@ ToolButton[toolbar-look="true"]:pressed
 }
 
 /*TabWidget*/
+#tabbar
+{
+    qproperty-tabPadding: -1;
+}
+
 #tabbar-button-right
 {
     qproperty-icon: url(images/tab-right-arrow.png);

themes/windows/main.css

@@ -134,6 +134,7 @@
 {
     min-height: 30px;
     max-height: 30px;
+    qproperty-tabPadding: 3;
 }
 
 #tab-icon