GTK3 theme: Redesign check and radio widgets

src/themes/Kali/sass/gtk-sass/_common-tweaks.scss

@@ -54,6 +54,38 @@ switch {
   }
 }
 
+/*************************
+ * Check and Radio items *
+ *************************/
+check,
+radio {
+  $_c: if($variant=='light', white, darken($bg_color, 2%));
+  $_shadow: 0 1px 2px transparentize($shadow_color, 0.03);
+
+  background-image: linear-gradient(to bottom, $_c 20%, darken($_c, 2%) 90%);
+  box-shadow: $_shadow;
+
+  @at-root %check_radio_disabled,
+  &:disabled {
+    &, &:backdrop {
+      border-color: $borders_color;
+      background-image: image($bg_color);
+    }
+  }
+
+  @each $t in (':checked'), (':indeterminate') {
+    &#{$t} {
+      background-image: linear-gradient(to bottom, $selected_bg_color 20%, darken($selected_bg_color, 2%) 90%);
+      border-color: $selected_borders_color;
+      box-shadow: inset 0 1px transparentize(white, .9), $_shadow;
+
+      &:active { box-shadow: none; }
+      &:backdrop { background-image: image($checkradio_bg_color); }
+      &:disabled { @extend %check_radio_disabled; }
+    }
+  }
+}
+
 /************
  * GtkScale *
  ************/