Added modern browser warning for theme support

postcss.config.js

@@ -0,0 +1,15 @@
+module.exports = {
+    plugins: [
+        require("postcss-import"),
+        require("autoprefixer")({
+            browsers: [
+                "Chrome >= 40",
+                "Firefox >= 35",
+                "Edge >= 14"
+            ]
+        }),
+        require("postcss-css-variables")({
+            preserve: true
+        }),
+    ]
+};