feat(cc-dark-theme): use sass instead of static css

In order to despaghettify the dark theme styles, this CL introduces Sass
compilation for the dark theme styles.

Bug: twpowertools:21
Change-Id: Ibbae3f85f355fab690f42f2bae9cf7766d9d43a3
diff --git a/templates/manifest.gjson b/templates/manifest.gjson
index cf8260b..8d067df 100644
--- a/templates/manifest.gjson
+++ b/templates/manifest.gjson
@@ -89,9 +89,9 @@
         "extraInfoInject.bundle.js",
         "litComponentsInject.bundle.js",
         "updateHandlerLitComponents.bundle.js",
+        "ccDarkTheme.bundle.css",
 
         "css/profileindicator_inject.css",
-        "css/ccdarktheme.css",
         "css/batchlock_inject.css",
         "css/enhanced_announcements_dot.css",
         "css/reposition_expand_thread.css",