Add project files.

ConstructorAppUI/wwwroot/AdminTheme/build/scss/_root.scss

@@ -0,0 +1,14 @@
+@include dark-mode () {
+  :root {
+    // Custom variable values only support SassScript inside `#{}`.
+    @each $color, $value in $colors-alt {
+      --#{$color}: #{$value};
+    }
+
+    @each $color, $value in $theme-colors-alt {
+      --#{$color}: #{$value};
+    }
+  }
+}
+
+//