.box21 {
    margin: 1em 0; /*altere 0 para auto para centralizar*/
     width: 80%; 
     /* largura */
}

.u01 {
    background: url(f-ue.gif) repeat-x;
    height: 23px;
    margin: 0 23px
}

.s01 {
    background: url(f-sita.gif) repeat-x;
    height: 23px;
    margin: 0 23px
}

.box-top {
    background-image: url(f-kado1.gif), url(f-kado2.gif);
    background-position: top left, top right;
    background-repeat: no-repeat, no-repeat;
    height: 23px;
}

.box-center {
    background-image: url(f-migi.gif), url(f-hidari.gif);
    background-position: top right, top left;
    background-repeat: repeat-y, repeat-y
}

.box-inner {
    background: #ffd6da;
    /* cor de fundo */
     margin: 0 23px
}

.box-bottom {
    background-image: url(f-kado3.gif), url(f-kado4.gif);
    background-position: top left, top right;
    background-repeat: no-repeat, no-repeat;
    height: 23px;
}