fix(dialog): fixed dialog color when dark theme elevation is enabled

Ref #1075

packages/dialog/src/_mixins.scss

@@ -50,9 +50,11 @@
 /// @access private
 @mixin rmd-dialog {
   @include rmd-elevation($rmd-dialog-elevation);
-  @include rmd-theme-dark-elevation($rmd-dialog-elevation);
-  @include rmd-theme-update-var(background, rmd-theme-var(surface));
-  @include rmd-theme(background-color, background);
+  @include rmd-dialog-theme(background-color);
+  @include rmd-theme-update-var(
+    background,
+    rmd-dialog-theme-var(background-color)
+  );
   @include rmd-theme(color, text-primary-on-background);
   @include rmd-utils-hide-focus-outline;
   @if mixin-exists(rmd-app-bar-theme-update-var) {

packages/dialog/src/_variables.scss

@@ -3,6 +3,8 @@
 ////
 
 @import '~@react-md/overlay/dist/variables';
+@import '~@react-md/theme/dist/variables';
+@import '~@react-md/theme/dist/functions';
 @import '~@react-md/utils/dist/variables';
 
 /// The elevation (box-shadow) to use for the dialog when it is not full page.
@@ -12,6 +14,44 @@
 /// @type Number
 $rmd-dialog-elevation: 16 !default;
 
+/// The background color for a dialog in light themes.
+///
+/// @type Color
+/// @since 2.7.0
+$rmd-dialog-light-background-color: rmd-theme-var(surface) !default;
+
+/// The background color for a dialog in dark themes when the
+/// `$rmd-theme-dark-elevation` feature flag is also enabled.
+///
+/// @see $rmd-theme-dark-elevation
+/// @require $rmd-theme-dark-elevation-colors
+/// @type Color
+/// @since 2.7.0
+$rmd-dialog-dark-elevation-background-color: map-get(
+  $rmd-theme-dark-elevation-colors,
+  $rmd-dialog-elevation
+) !default;
+
+/// The background color for a dialog in dark themes.
+///
+/// @type Color
+/// @since 2.7.0
+$rmd-dialog-dark-background-color: if(
+  $rmd-theme-dark-elevation and $rmd-dialog-dark-elevation-background-color,
+  $rmd-dialog-dark-elevation-background-color,
+  rmd-theme-var(surface)
+) !default;
+
+/// The base background color to apply to dialogs.
+///
+/// @type Color
+/// @since 2.7.0
+$rmd-dialog-background-color: if(
+  $rmd-theme-light,
+  $rmd-dialog-light-background-color,
+  $rmd-dialog-dark-background-color
+) !default;
+
 /// The z-index for dialogs. This value is a bit larger than overlays just in
 /// case other components are using the overlay as well. The dialog's overlay
 /// will also gain this z-index value.
@@ -77,6 +117,7 @@ $rmd-dialog-min-width: 17.5rem !default;
 /// of the icon as needed.
 /// @type Map
 $rmd-dialog-theme-values: (
+  background-color: $rmd-dialog-background-color,
   horizontal-margin: $rmd-dialog-horizontal-margin,
   vertical-margin: $rmd-dialog-vertical-margin,
   min-width: $rmd-dialog-min-width,

packages/theme/src/_mixins.scss

@@ -201,6 +201,16 @@
     );
   }
 
+  @if mixin-exists(rmd-dialog-theme-update-var) {
+    @if $rmd-dialog-light-background-color != $rmd-dialog-dark-background-color
+    {
+      @include rmd-dialog-theme-update-var(
+        background-color,
+        $rmd-dialog-light-background-color
+      );
+    }
+  }
+
   @if mixin-exists(rmd-divider-theme-update-var) {
     @include rmd-divider-theme-update-var(
       background-color,
@@ -375,6 +385,16 @@
     );
   }
 
+  @if mixin-exists(rmd-dialog-theme-update-var) {
+    @if $rmd-dialog-light-background-color != $rmd-dialog-dark-background-color
+    {
+      @include rmd-dialog-theme-update-var(
+        background-color,
+        $rmd-dialog-dark-background-color
+      );
+    }
+  }
+
   @if mixin-exists(rmd-divider-theme-update-var) {
     @include rmd-divider-theme-update-var(
       background-color,