HighContrast: Fix checkboxes in selected context

Set a proper color so checks and radios don't disappear on the
black selection background.

gtk/theme/HighContrast/_common.scss

@@ -1640,7 +1640,7 @@ GtkCheckButton.text-button, GtkRadioButton.text-button {
     color: $fg_color;
     background-image: none;
     -gtk-icon-source: -gtk-icontheme('#{$a}-symbolic');
-    &:hover { color: mix($fg_color, $bg_color, 80%) }
+    &:hover { color: $bg_color; }
     &:checked, &:active {
       -gtk-icon-source: -gtk-icontheme('#{$a}-checked-symbolic');
       &:disabled {

gtk/theme/HighContrast/gtk.css

@@ -1767,7 +1767,7 @@ check {
   background-image: none;
   -gtk-icon-source: -gtk-icontheme("checkbox-symbolic"); }
   check:hover {
-    color: #333333; }
+    color: #fff; }
   check:checked, check:active {
     -gtk-icon-source: -gtk-icontheme("checkbox-checked-symbolic"); }
     check:checked:disabled, check:active:disabled {
@@ -1792,7 +1792,7 @@ radio {
   background-image: none;
   -gtk-icon-source: -gtk-icontheme("radio-symbolic"); }
   radio:hover {
-    color: #333333; }
+    color: #fff; }
   radio:checked, radio:active {
     -gtk-icon-source: -gtk-icontheme("radio-checked-symbolic"); }
     radio:checked:disabled, radio:active:disabled {