add missing Slider to style.kv

gui/kivy/data/style.kv

@@ -46,6 +46,20 @@
     background_disabled_down: 'atlas://data/images/defaulttheme/bubble_btn_pressed'
     border: (0, 0, 0, 0)
 
+<Slider>:
+    canvas:
+        Color:
+            rgb: 1, 1, 1
+        BorderImage:
+            border: (0, 18, 0, 18) if self.orientation == 'horizontal' else (18, 0, 18, 0)
+            pos: (self.x + self.padding, self.center_y - sp(18)) if self.orientation == 'horizontal' else (self.center_x - 18, self.y + self.padding)
+            size: (self.width - self.padding * 2, sp(36)) if self.orientation == 'horizontal' else (sp(36), self.height - self.padding * 2)
+            source: 'atlas://data/images/defaulttheme/slider{}_background{}'.format(self.orientation[0], '_disabled' if self.disabled else '')
+        Rectangle:
+            pos: (self.value_pos[0] - sp(16), self.center_y - sp(17)) if self.orientation == 'horizontal' else (self.center_x - (16), self.value_pos[1] - sp(16))
+            size: (sp(32), sp(32))
+            source: 'atlas://data/images/defaulttheme/slider_cursor{}'.format('_disabled' if self.disabled else '')
+
 <RelativeLayout>:
     canvas.before:
         PushMatrix