Comments: SSO login icons too small to click on mobile when commenting

When viewing a site on mobile and making a comment on a post or page without being logged in, it offers the commenter several choices of Social Media account to log in to to leave the comment:

_Screen shot taken on desktop view_

On mobile, when someone is leaving a comment the social media login buttons are very small,
### What I expected:

Large, tappable social media icons to click on
### What happened instead

I see small, hard to click icons
### Steps to reproduce the issue:
1. Visit a blog post on a mobile device while not logged into WordPress.com or the site in question.
2. Go to leave a comment on the site.
3. See the small, hard to tap icons to log in to WP, FB, G+, and Twitter:

Seems the comments iframe isn't recognizing mobile, and should be made to be responsive.

Screenshots:
My test site:

_blog post [here](https://jacobshere.wpsandbox.me/2016/05/11/testing-an-email/), taken in Chrome's inspector_

Suggested by user in #2697114-t Screenshot from their ticket (they added their own icons):