how do I edit CSS for Disqus plugin?

I have been reading online all morning trying to figure out how to change the css for the Disqus plugin – when I make changes using firebug or the developer tool in google Chrome I can change the colors of text etc, but when I paste it to my CSS file – it does nothing. I found this one a website so I added it to my css to see if it changed anything – it did not:
/* — disqus css — */

#disqus_thread {
color: #ffffff;
border-style: 0px solid;
border-color: #cccccc;
padding: 5px;
}
#dsq-content #dsq-comments .dsq-comment-body {
color: #fff;
background-color: #C55B07;
}
.dsq-reaction-body {
color: #fff;
}
.dsq-reaction-header cite, .dsq-reaction-header span {
color: #ccc;
}
.dsq-reaction-retweets {
color: #ccc;
}
/*— end disqus css –*/

everything seems to refer back to a theme.css which appears to be located on the Disqus website. All I really want to do is change the color of text and hover colors so the plugin looks more like a natural part of my site – I have searched through the plugin folder and can’t seem to find a css file either – can someone please help me with this? Thank you!