Use Hugo extended for Sass/CSS (#13113)

Makefile

@@ -5,7 +5,7 @@ DOCKER_RUN   = $(DOCKER) run --rm --interactive --tty --volume $(CURDIR):/src
 NODE_BIN     = node_modules/.bin
 NETLIFY_FUNC = $(NODE_BIN)/netlify-lambda
 
-.PHONY: all build sass build-preview help serve
+.PHONY: all build build-preview help serve
 
 help: ## Show this help.
 	@awk 'BEGIN {FS = ":.*?## "} /^[a-zA-Z_-]+:.*?## / {sub("\\\\n",sprintf("\n%22c"," "), $$2);printf "\033[36m%-20s\033[0m %s\n", $$1, $$2}' $(MAKEFILE_LIST)
@@ -29,12 +29,6 @@ production-build: check-hugo-versions build check-headers-file ## Build the prod
 non-production-build: test-examples check-hugo-versions ## Build the non-production site, which adds noindex headers to prevent indexing
 	hugo --enableGitInfo
 
-sass-build:
-	scripts/sass.sh build
-
-sass-develop:
-	scripts/sass.sh develop
-
 serve: ## Boot the development server.
 	hugo server --buildFuture