fix(material/stepper): add styling to stepper for high contrast mode

Author: amysorto

src/material/stepper/_stepper-theme.scss

@@ -5,6 +5,7 @@
 @use '../core/typography/typography-utils';
 @use '../core/density/private/compatibility';
 @use './stepper-variables';
+@use '../../cdk/a11y';
 
 @mixin color($config-or-theme) {
   $config: theming.get-color-config($config-or-theme);
@@ -15,6 +16,19 @@
   $warn: map.get($config, warn);
 
   .mat-step-header {
+    @include a11y.high-contrast(active, off) {
+      outline: solid 1px;
+      &.cdk-keyboard-focused, &.cdk-program-focused {
+        outline: solid 3px;
+      }
+
+      &[aria-selected='true'] {
+        .mat-step-label {
+          text-decoration: underline;
+        }
+      }
+    }
+
     &.cdk-keyboard-focused,
     &.cdk-program-focused,
     &:hover:not([aria-disabled]),
@@ -100,6 +114,12 @@
     background-color: theming.get-color-from-palette($background, card);
   }
 
+  .mat-horizontal-content-container, .mat-vertical-content-container {
+    @include a11y.high-contrast(active, off) {
+      outline: solid 1px;
+    }
+  }
+
   .mat-stepper-vertical-line::before {
     border-left-color: theming.get-color-from-palette($foreground, divider);
   }