Add Mastodon

css/brands.css

@@ -155,6 +155,14 @@ button:hover,
 .button.button-linkedin:focus {
   filter: brightness(90%) }
 
+/* Mastodon */
+.button.button-mastodon {
+  color: #FFFFFF;
+  background-color: #1F232B }
+.button.button-mastodon:hover,
+.button.button-mastodon:focus {
+  filter: brightness(90%) }
+
 /* Medium */
 .button.button-medium {
   color: #FFFFFF;