refactor(Styles): Use mixins to make styles more DRY

.postcssrc

@@ -4,13 +4,16 @@
     "postcss-import": true,
     "postcss-import-url": { "modernBrowser": true },
     "postcss-url": { "url": "rebase" },
-    "postcss-nested": true,
+    "postcss-mixins": {
+      "mixinsDir": "src/common/styles/mixins"
+    },
     "postcss-custom-selectors": {
       "importFrom": "src/common/styles/selectors.css"
     },
     "postcss-custom-properties": {
       "preserve": false
     },
+    "postcss-nested": true,
     "autoprefixer": true
   }
 }

package.json

@@ -43,6 +43,7 @@
     "postcss-custom-selectors": "^5.1.2",
     "postcss-import": "^12.0.1",
     "postcss-import-url": "^4.0.0",
+    "postcss-mixins": "^6.2.2",
     "postcss-nested": "^4.1.2",
     "postcss-url": "^8.0.0",
     "prismjs": "^1.17.1",

src/common/styles/Article.css

@@ -0,0 +1,3 @@
+:--Article {
+  @mixin CreativeWork;
+}

src/common/styles/Entity.css

@@ -0,0 +1,8 @@
+:--Entity {
+  /*
+    Do not display `Entity` elements. These are a fallback
+    encoding for `Node` types which have no explicit HTML encoding yet
+    and contain only a JSON representation of the node.
+  */
+  display: none;
+}