style.css

body {
  font-family: sans-serif;
  text-align: center;
}

#output, textarea {
  border-style: solid;
  border-color: black;
  border-radius: 4px;
}

#output {
  overflow: auto;
  resize: both;
}

@media (prefers-color-scheme: dark) {
  body {
    color: white;
    background-color: black;
  }
  textarea, iframe {
    background-color: #aaaaaa;
  }
  a {
    color: #ADD8E6;
  }
  a:visited {
    color: #CBC3E3;
  }
}