rails--rails/guides/assets/stylesheets/dark.css

@media (prefers-color-scheme: dark) {

  :root {
    --text-color: #ddd;
    --text-red: #fc4343;
    --note-color: #fff9d8;
  }

  body {
    background-color: #222;
  }

  p code, ul code {
    background-color: #444;
    color: var(--text-color);
  }

  pre, code {
    color: #ddd;
  }

  table {
    background: #222;
  }

  tbody, thead {
    border: 2px solid #666;
  }

  table th {
    background-color: #333;
    border-bottom: 2px solid #666;
  }

  table th, table td {
    border: 1px solid #666;
  }

  #container {
    color: var(--text-color);
  }

  #feature {
    color: #eee;
    background: unset;
    background-color: #243440;
    border: 1px solid #d5e9f6;
    border-right: 0;
    border-left: 0;
  }

  #feature ul li {
    background-size: 1.4em 1.4em;
    background-image: url(../images/check_icon.svg);
    background-position: left 0.5em;
  }

  #mainCol a.anchorlink, #mainCol a.anchorlink code {
    color: #eee;
  }

  #mainCol a code, #subCol a code, #feature a code {
    color: var(--text-red);
  }

  #mainCol a, #subCol a, #feature a {
    color: #ee3f3f;
  }

  #subCol {
    background: #222;
    border: 1px solid #111;
  }

  #subCol .chapters {
    color: var(--text-red);
  }

  #subCol .chapters ul li {
    background-image: url(../images/bullet_dark.gif);
  }

  #subCol h3.chapter {
    padding-left:30px;
    background-image: url(../images/book_icon.svg);
    background-size: 1.25em;
    background-repeat: no-repeat;
  }

  #subCol h3.chapter img {
    display: none;
  }

  #mainCol div.warning, #subCol dd.warning {
    border: 1px solid #f9d9d8;
    background-color: #482928;
    background-image: url(../images/hand_icon.svg);
    background-size: 28px 28px;
    background-position: 10px 12px;
    color: #f9d9d8;
  }


  #footer {
    background-color: #000;
  }

  .note code, .info code, .todo code {
    background-color: #555;
  }

  .note {
    color: var(--note-color);
    border: 1px solid var(--note-color);
    background-color: #3e3b2c;
    background-image: url(../images/note_icon.svg);
    background-size: 28px 28px;
    background-position: 10px 10px;
  }

  #mainCol dd.work-in-progress, #subCol dd.work-in-progress {
    color: var(--note-color);
    border: 1px solid var(--note-color);
    background-color: #3e3b2c;
    background-image: url(../images/note_icon.svg);
    background-size: 28px 28px;
    background-position: 10px 10px;
  }

  .info, #mainCol dd.kindle, #subCol dd.kindle {
    border: 1px solid #d5e9f6;
    background-color: #243440;
    color: #d5e9f6;
    background-image: url(../images/info_icon.svg);
    background-size: 28px 28px;
    background-position: 10px 10px;
  }

  .clipboard-button {
    color: #ddd;
    background-color: #222;
  }

  div.code_container {
    /*background: none;*/
    background-color: #000;
    background-image: url(../images/cog_icon.svg);
    background-size: 28px 28px;
    background-position: 10px 14px;
    border: 1px solid #333;
  }
}