In the process of setting up my tumblr here I signed up for disqus.com to provide comments. Everything was going fine but then there were these really anoying borders between the profile and the comment box and at the bottom.

For some reason I REALLY wanted to get rid of these. After doing some digging I found they are actually a 50% transparent png background image which makes sense as this widget could be embedded almost anywhere.
After adding the following to my tumblr ‘Advanced’ ‘Custom CSS’ I have accomplished my goal.
#dsq-content div.dsq-options,
#dsq-content #dsq-new-post div.dsq-request-user-info,
#dsq-content #dsq-authenticate .dsq-login-buttons {
background-image: none;
margin: 0px;
padding-bottom: 10px;
}

Great Victory?
P.S.
In the process of writing this post I had need to include code using the trusty <pre> tag. My theme restyled <pre> with a variable spaced font which just doesn’t make sense. I fixed it like:
#container pre {
width: 484px;
margin: 0px 0px 14px -10px;
padding: 10px;
font-family: "Courier New", Courier, Monaco, monospace;
border: solid 8px #E1E1DA;
background-color: #EFEFEF;
}
This includes some theme info I added specifically for my theme but, if your theme did something similar and this is a problem you have, this should get started.