Customize Disqus
Repeating what @Assaf wrote but the current instructions for disqus styling are here.
They make it clear you can't style everything, only a few select things. For example for links you can set the color but not much else. I tried this on my own blog and it worked
#disqus_thread a { color: red;}
But I also tried this
#disqus_thread a { color: red; font-weight: bold; /* no effect */ text-decoration: underline; /* no effect */}
According to those docs, things you can set.
Choose the light or dark theme
It's set on the admin page under Admin > Setup > Appearance
Set the color of paragraphs and links
#disqus_thread p { color: green;}#disqus_thread a { color: red;}
Set the width of the comments
#disqus_thread { width: 700px;}
Add your logo if you pay for the Pro version
Reference: http://casadeblundell.com/jonathan/custom-styling-for-disqus-css/
/* --- 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: #000000;}.dsq-reaction-body {color: #fff;}.dsq-reaction-header cite, .dsq-reaction-header span {color: #ccc;}.dsq-reaction-retweets {color: #ccc;}/*--- end disqus css --*/