fix(material/core): improve disabled psuedo checkbox contrast

Author: Andrew Seguin

src/material/core/selection/pseudo-checkbox/_m2-pseudo-checkbox.scss

@@ -11,8 +11,6 @@
 
 // Tokens that can be configured through Angular Material's color theming API.
 @function get-color-tokens($theme, $color-variant) {
-  $is-dark: inspection.get-theme-type($theme) == dark;
-  $disabled-color: if($is-dark, #686868, #b0b0b0);
   $system: m2-utils.get-system($theme);
   $system: m3-utils.replace-colors-with-variant($system, secondary, $color-variant);
 
@@ -21,10 +19,13 @@
     pseudo-checkbox-full-selected-checkmark-color: map.get($system, background),
     pseudo-checkbox-full-unselected-icon-color: map.get($system, on-surface-variant),
     pseudo-checkbox-full-disabled-selected-checkmark-color: map.get($system, background),
-    pseudo-checkbox-full-disabled-unselected-icon-color: $disabled-color,
-    pseudo-checkbox-full-disabled-selected-icon-color: $disabled-color,
+    pseudo-checkbox-full-disabled-unselected-icon-color:
+    m3-utils.color-with-opacity(map.get($system, on-surface), 38%),
+    pseudo-checkbox-full-disabled-selected-icon-color:
+    m3-utils.color-with-opacity(map.get($system, on-surface), 38%),
     pseudo-checkbox-minimal-selected-checkmark-color: map.get($system, secondary),
-    pseudo-checkbox-minimal-disabled-selected-checkmark-color: if($is-dark, #686868, #b0b0b0),
+    pseudo-checkbox-minimal-disabled-selected-checkmark-color:
+    m3-utils.color-with-opacity(map.get($system, on-surface), 38%),
   );
 }