If you're using one of the default themes, in css/layout.css there should be something like:

#CommentHolder ul {
   list-style: none;
   margin: 20px 0;
}

#PageComments li {
   margin: 5px 0;
   padding: 1px;
   width: 88%;
}
#PageComments li.odd {
   background: #E8F6FF url(../images/commentBg.png) no-repeat 1% 10%;
   padding-left: 40px;
   padding-right: 10px;
   border-bottom: 2px solid #BCE4FE;
}

#PageComments li.even {
   background: #fff url(../images/commentBgAlt.png) no-repeat 99% 10%;
   padding-right: 40px;
   padding-left: 10px;
}

#PageComments li.odd p.info {
   color: #3AA0C3;
}

.actionLinks li a {
   padding-right: 3px;
   font-size: 10px;
}
.actionLinks li {
display: inline;
border-right: 1px solid;
}
.actionLinks li.last {
border-right: none;
}

.commentrss {
   background: transparent url(../images/feed-icon-14x14.png) no-repeat;
   padding-left: 20px;
   font-size: 1.1em;
   line-height: 1.6em;
}
#PageCommentsPagination p {
   text-align: center;
   font-size: 1.2em;
}
#PageComments p {
   font-size: 1em;
}
#PageComments p.info {
   color: #999;
   margin: 0px;
   padding: 0;
   line-height: 1em;
   font-size: 0.9em;
}

if there is, just modify it the way you want. If it's not, insert this part of code and then modify it the way you like