common/modules/comment/resources/comment.css

.artbox_comment_reply_author, .artbox_comment_update_reply {
    position: relative;
    width: 25%;
}
.artbox_comment_update_reply {
    width: 25%;
    float: none;
}
.artbox_comment_reply_author:after, .artbox_comment_update_reply:after {
    content: '';
    background-image: url('delete-ico.png');
    display: block;
    position: absolute;
    right: -13px;
    width: 13px;
    height: 13px;
    top: 0;
    cursor: pointer;
}