.pdf-wrapper {
  width: 100%;
  max-width: 900px;   /* optional */
  margin: 1rem auto;
  border: 6px solid gray;
  box-sizing: border-box;
}

.pdf-wrapper iframe {
  width: 100%;
  height: 100%;
  border: 0;
  display: block;
}

/* 3:4 portrait-ish preview (good for books) */
.ratio-3-4 {
  aspect-ratio: 3 / 4;
}

/* Optional: reduce height impact on small screens */
@media (max-width: 600px) {
  .ratio-3-4 {
    aspect-ratio: 1 / 1.2; /* a bit less tall on phones */
  }
  .pdf-wrapper {
    border-width: 3px;
  }
}