odoo/addons/mail/static/src/css/mail.css

/** ThreadView widget **/

.oe_mail_comment {
    width: 65%;
    border: 4px solid #770033;
}

.oe_mail_msg {
    width: 80%;
    border: 4px solid #998877;
}

.oe_mail_msg:after {
  content: "";
  display: block;
  clear: both; 
}

.oe_mail_msg_image {
    float: left;
    width: 10%;
}

.oe_mail_msg_content {
    float: right;
    width: 80%;
    border: 4px solid #557722;
}

.oe_mail_msg_body {
}

.oe_mail_msg_author {
}

.oe_mail_msg_date {
}

.oe_mail_msg_p {
    padding: 0;
    margin: 0;
    width: 25%;
    word-wrap: break-word;
}