Distorted "accept" post – MailChimp plugin

Hi all,
I’m getting a super weirdly distorted “acceptance post” from my MailChimp plugin where it’s rather out of place.

Here’s a screenshot: https://drive.google.com/file/d/0B2UxOY-hpfPMM2w1RXpKRDkxTlBwcjN3Ym5XMnpzTW1RLWRN/view?usp=sharing

Any thoughts on how to solve this? Tried the following and it didn’t work:
.mc4wp-success {overflow: hidden;}