Update tailwind to v3, various wangling

theme/static_src/tailwind.config.js

@@ -2,14 +2,10 @@
 // If you need the full config, get it from here:
 // https://unpkg.com/browse/tailwindcss@latest/stubs/defaultConfig.stub.js
 module.exports = {
-    purge: [
-        // Templates within theme app (e.g. base.html)
+    content: [
         '../templates/**/*.html',
-        // Templates in other apps. Uncomment the following line if it matches
-        // your project structure or change it to match.
         '../../templates/**/*.html',
     ],
-    darkMode: 'media',
     theme: {
         extend: {},
     },