Change Included "Green Button" Style to Different Color

Hi all,

Simple question here. I need to change the color of the "Green Button" under the style settings. I grabbed the CSS for this element and put it in my theme's style.css file expecting it to override the plugin CSS but it's not working.

Here's what I used...including my changed hex color:

a.wdca_button {
    color: #FFFFFF !important;
    text-shadow: -1px -1px 0 #8DB74B;
}

Shouldn't this be enough to change the button color? If not, do you have any advice on how to best specify a button color?