Improve tests for Tailwind CSS v3 (#252)

* Adjust tailwind.config.js to match v3 (drop purge: entry)

* Adjust tests to tw3 non-alpha output

* run prettier on test file

* rename `twVariables` to `defaults`

This is more inline with what we do in the tailwindcss codebase itself

* embed the `${defaults}` directly

Co-authored-by: Ingo Struck (git commits) <gitlab@ingostruck.de>

Author: RobinMalfait

demo/tailwind.config.js

@@ -1,11 +1,9 @@
 const mdx = require('@mdx-js/mdx')
 
 module.exports = {
-  purge: {
-    content: ['./demo/pages/**/*.{js,mdx}', './demo/components/**/*.{js,mdx}'],
-    transform: {
-      mdx: (content) => mdx.sync(content),
-    },
+  content: ['./demo/pages/**/*.{js,mdx}', './demo/components/**/*.{js,mdx}'],
+  transform: {
+    mdx: (content) => mdx.sync(content),
   },
   theme: {
     extend: {