Styling the subscribe button on widget

If you visit my website: http://aaronmoritz.net , you will see that I have applied some style elements to the ‘subscribe’ button, on the right hand sidebar widget for e-mail subscriptions.

My issue is that the subscribe button has no ‘id’ or ‘class’ settings that I can utilize to style it with css, so I end up just editing the plugin php files themselves to add an id manually.

This of course leads to the incredibly tedious issue of having to do this every time the plugin updates.

Is there an easier way I could be doing this? I sent an email ot the jetback dev team asking if some ‘id’ could be included for this button in the plugin itself, but got no response.

https://wordpress.org/plugins/jetpack/