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