update category display in menu

static/css/site.css

@@ -170,6 +170,14 @@ ul, ol {
   text-align: center;
 }
 
+#categories {
+  margin-top: 40px;
+}
+
+#categories:before {
+  content: "Categories:";
+}
+
 #contentinfo {
   flex-shrink: 0;
   margin-top: 40px