feat(dialog): add custom property for z-index

PiperOrigin-RevId: 349484781

Author: Elliott Marquez

packages/mdc-dialog/_dialog-custom-properties.scss

@@ -0,0 +1,23 @@
+//
+// Copyright 2020 Google Inc.
+//
+// Permission is hereby granted, free of charge, to any person obtaining a copy
+// of this software and associated documentation files (the "Software"), to deal
+// in the Software without restriction, including without limitation the rights
+// to use, copy, modify, merge, publish, distribute, sublicense, and/or sell
+// copies of the Software, and to permit persons to whom the Software is
+// furnished to do so, subject to the following conditions:
+//
+// The above copyright notice and this permission notice shall be included in
+// all copies or substantial portions of the Software.
+//
+// THE SOFTWARE IS PROVIDED "AS IS", WITHOUT WARRANTY OF ANY KIND, EXPRESS OR
+// IMPLIED, INCLUDING BUT NOT LIMITED TO THE WARRANTIES OF MERCHANTABILITY,
+// FITNESS FOR A PARTICULAR PURPOSE AND NONINFRINGEMENT. IN NO EVENT SHALL THE
+// AUTHORS OR COPYRIGHT HOLDERS BE LIABLE FOR ANY CLAIM, DAMAGES OR OTHER
+// LIABILITY, WHETHER IN AN ACTION OF CONTRACT, TORT OR OTHERWISE, ARISING FROM,
+// OUT OF OR IN CONNECTION WITH THE SOFTWARE OR THE USE OR OTHER DEALINGS IN
+// THE SOFTWARE.
+//
+
+$z-index: --mdc-dialog-z-index;

packages/mdc-dialog/_mixins.scss

@@ -30,10 +30,12 @@
 @use '@material/feature-targeting/feature-targeting';
 @use '@material/rtl/mixins' as rtl-mixins;
 @use '@material/shape/mixins' as shape-mixins;
+@use '@material/theme/custom-properties';
 @use '@material/theme/theme';
 @use '@material/theme/theme-color';
 @use '@material/touch-target/variables' as touch-target-variables;
 @use '@material/typography/typography';
+@use './dialog-custom-properties';
 @use './variables';
 
 @mixin core-styles($query: feature-targeting.all()) {
@@ -78,7 +80,11 @@
     @include feature-targeting.targets($feat-structure) {
       // Use `display: none` instead of `visibility: hidden` to avoid recalculating layout when the dialog is closed.
       display: none;
-      z-index: variables.$z-index;
+      $z-index: custom-properties.create(
+        dialog-custom-properties.$z-index,
+        variables.$z-index
+      );
+      @include theme.property(z-index, $z-index);
     }
   }