[gnome-shell-sass] theme: darken sliders to match gtk

[Florian Müllner <fmuellner src gnome org>]

commit e14084eb9a00b086e760dc5066d4e4d0c2c16597
Author: Jakub Steiner <jimmac gmail com>
Date:   Wed Jun 26 12:34:42 2019 +0200

    theme: darken sliders to match gtk
    
    - match gtk a bit more closely, but avoid the gradients (change will
      happen on gtk side for this one).

 _common.scss | 3 +--
 1 file changed, 1 insertion(+), 2 deletions(-)
---
diff --git a/_common.scss b/_common.scss
index e400142..32a6df7 100644
--- a/_common.scss
+++ b/_common.scss
@@ -146,8 +146,7 @@ StScrollBar {
   -slider-handle-radius: 8px;
   -slider-handle-border-width: 1px;
   -slider-handle-border-color: $borders_color;
-  color: $bg_color; /* FIXME to match gtk, we'd need to style the border of the slider, not
-     the whole widget */
+  color: if($variant == 'light', lighten($bg_color, 10%), darken($bg_color,4%));
   &:hover { color: $_hover_bg_color; }
   &:active { color: $_active_bg_color; }
 }