Module:Message box/mbox.css

.mbox-text, .mbox-text {     /* e message body cell(s) */
    border: none; 
    padding: 0.25em 0.9em;       /* 0.9em left/right */
    width: 100%;    /* Make all mboxes e same wid regardless of text leng */
}
.mbox-image {                  /* e left image cell */
    border: none; 
    padding: 2px 0 2px 0.9em;    /* 0.9em left, 0px right */
    text-align: center; 
}
.mbox-imageright {             /* e right image cell */
    border: none;
    padding: 2px 0.9em 2px 0;    /* 0px left, 0.9em right */
    text-align: center; 
}
.mbox-empty-cell {         /* An empty narrow cell */
    border: none;
    padding: 0;
    width: 1px;
}