Add this style in your theme css file.
May be few modifications in this style will solve your issue.
ol.commentlist { list-style:none; margin:0; padding:0; text-indent:0; }
ol.commentlist li { border:1px solid #d5d5d5; border-radius:5px; -moz-border-radius:5px; -webkit-border-radius:5px; height:1%; margin:0 0 10px; padding:5px 7px 5px 57px; position:relative; }
ol.commentlist li.alt { }
ol.commentlist li.bypostauthor {}
ol.commentlist li.byuser {}
ol.commentlist li.comment-author-admin {}
ol.commentlist li.comment { }
ol.commentlist li div.comment-author { padding:0 447px 0 0; }
ol.commentlist li div.vcard { font:bold 14px/1.4 helvetica,arial,sans-serif; padding-left:5px; }
ol.commentlist li div.vcard cite.fn { font-style:normal; }
ol.commentlist li div.vcard cite.fn a.url { color:#c00; text-decoration:none; }
ol.commentlist li div.vcard cite.fn a.url:hover { color:#000; }
ol.commentlist li div.vcard img.avatar { border:5px solid #d5d5d5; left:7px; position:absolute; top:7px; }
ol.commentlist li div.vcard img.avatar-32 {}
ol.commentlist li div.vcard img.photo {}
ol.commentlist li div.vcard span.says {}
ol.commentlist li div.commentmetadata {}
ol.commentlist li div.comment-meta { font:bold 10px/1.4 helvetica,arial,sans-serif; position:absolute; right:10px; text-align:right; top:5px; }
ol.commentlist li div.comment-meta a { color:#333; text-decoration:none; }
ol.commentlist li div.comment-meta a:hover { color:#000; }
ol.commentlist li p { font:normal 12px/1.4 helvetica,arial,sans-serif; margin:0 0 1em; padding-left:5px; }
ol.commentlist li ul { font:normal 12px/1.4 helvetica,arial,sans-serif; list-style:square; margin:0 0 1em; padding:0; text-indent:0; }
ol.commentlist li div.reply { background:#999; border:1px solid #666; border-radius:2px; -moz-border-radius:2px; -webkit-border-radius:2px; color:#fff; font:bold 9px/1 helvetica,arial,sans-serif; padding:5px 10px; text-align:center; float:right; width:69px; z-index:9999; bottom:8px; position:absolute; right:5px;}
ol.commentlist li div.reply:hover { background:#c30; border:1px solid #c00; }
ol.commentlist li div.reply a { color:#fff; text-decoration:none; text-transform:uppercase; }
ol.commentlist li ul.children { list-style:none; margin:1em 0 0; text-indent:0; }
ol.commentlist li ul.children li { }
ol.commentlist li ul.children li.alt {}
ol.commentlist li ul.children li.bypostauthor {}
ol.commentlist li ul.children li.byuser {}
ol.commentlist li ul.children li.comment {}
ol.commentlist li ul.children li.comment-author-admin {}
ol.commentlist li ul.children li.depth-2 { margin:0 0 .25em; }
ol.commentlist li ul.children li.depth-3 { margin:0 0 .25em; }
ol.commentlist li ul.children li.depth-4 { margin:0 0 .25em; }
ol.commentlist li ul.children li.depth-5 {}
ol.commentlist li ul.children li.odd {}
ol.commentlist li.even { background:#fff; height:auto; }
ol.commentlist li.odd { background:#f6f6f6; height:auto;}
ol.commentlist li.parent { }
ol.commentlist li.pingback { }
ol.commentlist li.pingback.parent { }
ol.commentlist li.pingback div.vcard { padding:0 170px 0 0; }
ol.commentlist li.thread-alt { }
ol.commentlist li.thread-even {}
ol.commentlist li.thread-odd {}