h3#invalid ~ pre:not(h3#valid ~ pre) {
  background-color: #f4e7e7;
  border: 2px solid #ec8282;
}

h3#valid ~ pre {
  background-color: #e9f0db;
  border: 2px solid #72c072;
}

@media (prefers-color-scheme: dark) {
  body {
    background-color: #0d1117;
    color: #ffffff;
  }

  h3#invalid ~ pre:not(h3#valid ~ pre) {
    background-color: #221616;
    border: 2px solid #aa3f3f;
  }

  h3#valid ~ pre {
    background-color: #1b2216;
    border: 2px solid #406e40;
  }
}