.box-vintage{
  position:relative;
  background:#f7f1e3;
  border:2px solid #5a3e2b;
  padding:24px;
}

/* Filetto interno “a cornice” con angoli vuoti */
.box-vintage::after{
  --gap:12px;              /* profondità angolo */
  --off:8px;               /* distanza dal bordo esterno */
  content:"";
  position:absolute;
  left:var(--off); right:var(--off);
  top:var(--off); bottom:var(--off);
  pointer-events:none;
  background:
    /* lato sinistro (lascia buco agli angoli) */
    linear-gradient(#5a3e2b,#5a3e2b) top    var(--gap) left 0/1px calc(100% - 2*var(--gap)) no-repeat,
    /* lato superiore */
    linear-gradient(#5a3e2b,#5a3e2b) top 0 right var(--gap)/calc(100% - 2*var(--gap)) 1px no-repeat,
    /* lato destro */
    linear-gradient(#5a3e2b,#5a3e2b) bottom var(--gap) right 0/1px calc(100% - 2*var(--gap)) no-repeat,
    /* lato inferiore */
    linear-gradient(#5a3e2b,#5a3e2b) bottom 0 left var(--gap)/calc(100% - 2*var(--gap)) 1px no-repeat;
}