fix: background color behind mastodon share button

Signed-off-by: thiswillbeyourgithub <[email protected]>

Author: thiswillbeyourgithub

_sass/layout/_buttons.scss

@@ -119,6 +119,7 @@
 
   $social:
   (bluesky, $bluesky-color),
+  (mastodon, $mastodon-color),
   (facebook, $facebook-color),
   (twitter, $twitter-color),
   (google-plus, $google-plus-color),