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/package.json b/package.json
index 6ed1914..8afee5a 100644
--- a/package.json
+++ b/package.json
@@ -33,6 +33,7 @@
     "jest": "^29.3.1",
     "jest-environment-jsdom": "^29.3.1",
     "json5": "^2.2.0",
+    "mini-css-extract-plugin": "^2.7.6",
     "path": "^0.12.7",
     "raw-loader": "^4.0.2",
     "sass": "^1.38.1",