reintroduce contextual styles

Author: ttaylor-stack

packages/stacks-classic/lib/components/button/button.less

@@ -56,6 +56,14 @@
     --_bu-number-fc-filled: var(--theme-button-primary-number-color, var(--theme-secondary-600));
     --_bu-number-fc-selected: var(--white);
 
+    // CONTEXTUAL STYLES
+    .highcontrast-mode({
+        --_bu-bc: currentColor;
+        --_bu-fc-selected: var(--white);
+        --_bu-badge-o: 0.8;
+        --_bu-number-fc-selected: var(--theme-button-primary-number-color, var(--theme-secondary-600));
+    });
+
     // STATES
     fieldset[disabled] &,
     &[disabled],