refactor: move mat-app-background out of core

src/dev-app/theme.scss

@@ -25,6 +25,7 @@ $candy-app-theme: mat.m2-define-light-theme((
 // have to load a single css file for Angular Material in your app.
 // **Be sure that you only ever include this mixin once!**
 @include mat.core();
+@include mat.app-background();
 
 // Include the default theme styles.
 @include mat.all-component-themes($candy-app-theme);

src/material/_index.scss

@@ -36,7 +36,7 @@
 @forward './core/style/validation' as private-*;
 
 // Structural
-@forward './core/core' show core;
+@forward './core/core' show core, app-background;
 @forward './core/ripple/ripple' show ripple;
 @forward './core/focus-indicators/private' show strong-focus-indicators,
   strong-focus-indicators-color, strong-focus-indicators-theme;

src/material/core/_core.scss

@@ -22,11 +22,6 @@
   @at-root {
     // Note: we need to emit fallback values here to avoid errors in internal builds.
     @include token-utils.use-tokens(tokens-mat-app.$prefix, tokens-mat-app.get-token-slots()) {
-      .mat-app-background {
-        @include token-utils.create-token-slot(background-color, background-color, transparent);
-        @include token-utils.create-token-slot(color, text-color, inherit);
-      }
-
       // Provides external CSS classes for each elevation value. Each CSS class is formatted as
       // `mat-elevation-z$z-value` where `$z-value` corresponds to the z-space to which the element
       // is elevated.
@@ -42,3 +37,15 @@
     }
   }
 }
+
+// Mixin that provides the .mat-app-background class.
+@mixin app-background() {
+  @at-root {
+    @include token-utils.use-tokens(tokens-mat-app.$prefix, tokens-mat-app.get-token-slots()) {
+      .mat-app-background {
+        @include token-utils.create-token-slot(background-color, background-color, transparent);
+        @include token-utils.create-token-slot(color, text-color, inherit);
+      }
+    }
+  }
+}

src/universal-app/styles.scss

@@ -1,6 +1,7 @@
 @use '@angular/material' as mat;
 
 @include mat.core();
+@include mat.app-background();
 
 $theme: mat.define-theme((
   color: (