[chore] update dependencies and modernize postcss config

.postcssrc.js

@@ -0,0 +1,27 @@
+const url = require("postcss-url");
+const imports = require("postcss-import");
+const nested = require("postcss-nested");
+const postCSSPresetEnv = require("postcss-preset-env");
+const cssnano = require("cssnano");
+const color = require("postcss-color-mod-function");
+const mixins = require("postcss-mixins");
+
+module.exports = () => ({
+  plugins: [
+    url,
+    imports,
+    mixins,
+    nested,
+    postCSSPresetEnv({
+      stage: 1,
+      preserve: true,
+      features: {
+        "custom-properties": true,
+      },
+    }),
+    cssnano({
+      preset: "default",
+    }),
+    color,
+  ],
+});