Change floating action button to be a button in header in web UI (#19422)

- Fix theme color
- Fix elephant being too big on error page on small screens
- Remove "Follows and Followers" link from navigation panel

app/javascript/mastodon/features/ui/index.js

@@ -145,7 +145,7 @@ class SwitchingColumnsArea extends React.PureComponent {
 
   setRef = c => {
     if (c) {
-      this.node = c.getWrappedInstance();
+      this.node = c;
     }
   }