/* Your existing container style */
#content1 {
  margin: auto;
  max-width: 600px;
  padding: 20px;
  border: groove 5px black;
}

/* Audio elements */
audio {
  display: block;
  width: 90%;
  max-width: 1024px;
  margin: 0 auto 10px;
}

/* Responsive tweaks */
@media (max-width: 600px) {
  #content1 {
    padding: 10px;      /* a little tighter on phones */
  }
  audio {
    max-width: 100%;    /* let players stretch fully on small devices */
  }
}