Dark theme: Fix selected sidebar button background

One of my recent changes must have broken the selected background color.

Change-Id: I4ed79b29193bddb4423273f65562d20e54361f9a
Reviewed-by: Alessandro Portale <alessandro.portale@theqtcompany.com>

share/qtcreator/themes/dark.creatortheme

@@ -47,7 +47,7 @@ FancyTabWidgetDisabledUnselectedTextColor=textDisabled
 FancyTabWidgetEnabledSelectedTextColor=text
 FancyTabWidgetEnabledUnselectedTextColor=text
 FancyToolButtonHoverColor=35ffffff
-FancyToolButtonSelectedColor=66000000
+FancyToolButtonSelectedColor=7effffff
 FutureProgressBackgroundColor=shadowBackground
 IconsBaseColor=ffdcdcdc
 IconsDisabledColor=textDisabled