This is a style that I used for a client on the Nuru template but at the very least shows you the classes you need to alter.

/* JComments Wrapper */
#jc {
	padding: 5px;
	border-bottom-left-radius: 25px;
	border-bottom-right-radius: 25px;
	background-color: #220203;
	/*border: 1px solid #DBB054;*/
	max-width: 1070px;
	margin: 0 auto;
}

/* Comment Box */
#jc .rbox {
	background: transparent;
	border: none;  
	padding: 10px;
	border-top: 1px dotted #ee9200; 
	border-radius: 0px;
	margin-top: 20px;
	margin-bottom: 20px;
}

/* Comment Content - Set Font for the comments */
#jc .comment-body{
  font-family: Georgia,"Times New Roman",Times,serif;
  font-size: 18px;
  line-height: 22px;
  color: #ee9200;
  text-align: left;
  margin-bottom: 20px;
}

/* Latest Module */
.jcomments-latest {
	font-family: Georgia,"Times New Roman",Times,serif;
	font-size: 18px;
	line-height: 22px;
	color: #ee9200;
	padding: 20px !important;
	border-radius: 25px;
	background-color: #220203;
	border: 1px solid #DBB054;
}

/* Latest Module - Rounded Corners */
ul.jcomments-latest .rounded {
	padding: 20px !important;
	border: none !important;
	border-top: 1px dotted #ee9200 !important;
    -moz-border-radius: 5px;
    border-radius: 0px !important;
	margin-top: 20px;
}