Use webpack and postcss to generate CSS

package.json

@@ -5,15 +5,25 @@
     "repository": "https://github.com/jonnybarnes/jonnybarnes.uk",
     "license": "CC0-1.0",
     "dependencies": {
+        "cssnano": "^4.1.10",
         "normalize.css": "^8.0.1",
+        "postcss-import": "^13.0.0",
         "puppeteer": "^5.3.1",
         "stylelint-a11y": "^1.2.3"
     },
     "devDependencies": {
+        "@gfx/zopfli": "^1.0.15",
+        "autoprefixer": "^9.8.6",
+        "browserlist": "^1.0.1",
+        "compression-webpack-plugin": "^6.1.1",
         "css-loader": "^5.0.0",
         "husky": "^4.3.0",
         "lint-staged": "^10.4.0",
         "mini-css-extract-plugin": "^1.0.0",
+        "postcss": "^8.1.6",
+        "postcss-combine-duplicated-selectors": "^10.0.2",
+        "postcss-combine-media-query": "^1.0.1",
+        "postcss-loader": "^4.0.4",
         "pre-commit": "^1.1.3",
         "stylelint": "^13.7.2",
         "stylelint-config-standard": "^20.0.0",
@@ -44,5 +54,11 @@
         "*.scss": [
             "stylelint --syntax=scss"
         ]
-    }
+    },
+    "browserslist": [
+        "last 2 versions",
+        "> 1%",
+        "not IE 11",
+        "not IE_Mob 11"
+    ]
 }