configure purgecss to accept tailwindcss classnames

* like ".w-1/6" which is ignored and purged by default
* currently we have to define all filetypes used in our project due to
  missing DefaultExtractor fallback by purgecss
  (FullHuman/purgecss#148)

next.config.js

@@ -7,6 +7,25 @@ const config = {
 		CONTENT_HOST: "http://localhost:3000",
 		BASE_PATH: process.env.BASE_PATH || "",
 	},
+	purgeCss: {
+		extractors: [
+			{
+				extractor: class TailwindExtractor {
+					static extract(content) {
+						return content.match(/[A-Za-z0-9:/_-]+/g) || [];
+					}
+				},
+				extensions: ["tailwind.css", "js", "jsx", "svg"].concat([
+					// TODO remove extensions as soon as DefaultExtractor fallback exists in purgecss.
+					//      see https://github.com/FullHuman/purgecss/issues/148
+					"jpg",
+					"jpeg",
+					"png",
+					"gif",
+				]),
+			},
+		],
+	},
 	assetPrefix: process.env.ASSET_PREFIX || "",
 };