fix(material/datepicker): date ranges not visible in high contrast mode (#23038)

Fixes that the date ranges are invisible in high contrast mode.

Fixes #23034.

Author: crisbeto

src/material/datepicker/calendar-body.scss

@@ -194,8 +194,11 @@ $calendar-range-end-body-cell-size:
 }
 
 @include a11y.high-contrast(active, off) {
+  $main-range-border: solid 1px;
+  $comparison-range-border: dashed 1px;
+
   .mat-datepicker-popup:not(:empty),
-  .mat-calendar-body-selected {
+  .mat-calendar-body-cell:not(.mat-calendar-body-in-range) .mat-calendar-body-selected {
     outline: solid 1px;
   }
 
@@ -209,6 +212,61 @@ $calendar-range-end-body-cell-size:
       outline: dotted 2px;
     }
   }
+
+  // These backgrounds need to be removed, because they'll block the date ranges.
+  .mat-calendar-body-cell::before,
+  .mat-calendar-body-cell::after,
+  .mat-calendar-body-selected {
+    background: none;
+  }
+
+  .mat-calendar-body-in-range::before,
+  .mat-calendar-body-comparison-bridge-start::before,
+  .mat-calendar-body-comparison-bridge-end::before {
+    border-top: $main-range-border;
+    border-bottom: $main-range-border;
+  }
+
+  .mat-calendar-body-range-start::before {
+    border-left: $main-range-border;
+
+    [dir='rtl'] & {
+      border-left: 0;
+      border-right: $main-range-border;
+    }
+  }
+
+  .mat-calendar-body-range-end::before {
+    border-right: $main-range-border;
+
+    [dir='rtl'] & {
+      border-right: 0;
+      border-left: $main-range-border;
+    }
+  }
+
+  .mat-calendar-body-in-comparison-range::before {
+    border-top: $comparison-range-border;
+    border-bottom: $comparison-range-border;
+  }
+
+  .mat-calendar-body-comparison-start::before {
+    border-left: $comparison-range-border;
+
+    [dir='rtl'] & {
+      border-left: 0;
+      border-right: $comparison-range-border;
+    }
+  }
+
+  .mat-calendar-body-comparison-end::before {
+    border-right: $comparison-range-border;
+
+    [dir='rtl'] & {
+      border-right: 0;
+      border-left: $comparison-range-border;
+    }
+  }
 }
 
 [dir='rtl'] {