Yes I show you with instructions.

1. Edit the class of the button in the Mailchimp form code to what you see in this screenshot, https://www.dropbox.com/s/20wuthonx7588g0/2017-02-12.png?dl=0

2. Delete the following css code from the style.css file (line 1150 to 1170)

#mc-embedded-subscribe-form input[type="submit"],
.ctct-embed-signup .ctct-button {
background-color: #00aded;
border: 0;
color: #fff;
display: inline-block;
font-size: 1.071rem;
font-weight: 400;
text-transform: uppercase;
text-decoration: none;
cursor: pointer;
margin-bottom: 20px;
line-height: normal;
letter-spacing: 2px;
border-radius: 4px;
}
#mc-embedded-subscribe-form input[type="submit"]:hover,
.ctct-embed-signup .ctct-button:hover {
color: #333;
background-color: #fff;
}

3. Delete the following code from the /inc/options.php file (line 411 and 412)

#mc-embedded-subscribe-form input[type="submit"],

Let me know if that works.