Use tailwind with postcss

Author: RoyalIcing

apps/components_guide_web/assets/css/app.css

@@ -1,3 +1,9 @@
 /* This file is for your main application css. */
 
-@import "./phoenix.css";
+@tailwind base;
+
+@tailwind components;
+
+@tailwind utilities;
+
+/* @import "./phoenix.css"; */