[docs] Theme essential

Author: jamesgpearce

site/less/article.less

@@ -40,6 +40,15 @@ body > main > article {
   img[title^='Thumbnail'] {
     width: 50%;
   }
+  .essential {
+    background-color: @accentColor;
+    color: @backColor;
+    padding: 0.25rem;
+    border-radius: 0.25rem;
+    font-size: 0.8rem;
+    display: inline-block;
+    line-height: normal;
+  }
 }
 
 @media (min-width: 38rem) {