#mainbody {
    min-width: 980px;
    max-width: 1190px;
    margin: 0 auto;
}

.postattachlist {
    width: 100%;
}

/* change existing class to width:100% (@style_1.css) */
.postattachlist .t_attachlist dd p img {
    max-width: 100%;
}

.t_msgfont img {
    max-width: 100%;
    height: auto;
}