.chapter-rail {
  display: none;
}

@media (min-width: 1100px) {
  .chapter-trial-active .detail-tabs {
    display: none;
  }

  .chapter-trial-active .detail-layout {
    grid-template-columns: 156px minmax(0, 1fr) 250px;
    gap: 32px;
  }

  .chapter-rail {
    --chapter-step: 40px;
    display: block;
    position: sticky;
    top: 18px;
    align-self: start;
    z-index: 2;
    padding: 14px 12px 12px;
    border: 1px solid var(--paper-edge);
    border-radius: 10px;
    background: #fffdf8;
    box-shadow: 0 8px 24px #152d480a;
  }

  .chapter-rail-label {
    margin-bottom: 7px;
    color: #765830;
    font-size: 12px;
    font-weight: 600;
    letter-spacing: .1em;
  }

  .chapter-rail-list {
    position: relative;
    margin: 0;
    padding: 0 0 0 21px;
    list-style: none;
  }


  .chapter-rail-list::before,
  .chapter-rail-list::after,
  .chapter-hover-guide {
    position: absolute;
    top: 0;
    left: 4px;
    width: 12px;
    border-left: 1px dashed;
    pointer-events: none;
    content: "";
  }

  .chapter-rail-list::before {
    height: calc(100% - var(--chapter-step) / 2);
    color: #d1c5b4;
  }

  .chapter-rail-list::after,
  .chapter-hover-guide {
    border-bottom: 1px dashed;
    border-bottom-left-radius: 7px;
    transition: height .36s cubic-bezier(.22, .76, .31, 1), opacity .18s ease;
  }

  .chapter-rail-list::after {
    height: calc(var(--chapter-step) * (var(--chapter-index, 0) + .5));
    color: #8c5f30;
  }

  .chapter-hover-guide {
    height: calc(var(--chapter-step) * (var(--chapter-hover-index, 0) + .5));
    color: #ad9e88;
    opacity: 0;
  }

  .chapter-hover .chapter-hover-guide { opacity: 1; }

  .chapter-rail button {
    display: block;
    width: 100%;
    height: var(--chapter-step);
    padding: 0 9px;
    border: 0;
    border-radius: 6px;
    background: transparent;
    color: #4b5966;
    font-size: 13px;
    line-height: 1.3;
    text-align: left;
    transition: background-color .18s ease, color .18s ease;
  }

  .chapter-rail button:hover,
  .chapter-rail button[aria-current="location"] {
    background: #f4eddf;
    color: var(--navy);
  }

  .chapter-rail button[aria-current="location"] {
    font-weight: 600;
  }

  .chapter-sublist {
    margin: 0;
    padding: 0 0 0 11px;
    list-style: none;
  }

  .chapter-sublist button { font-size: 12px; }
  .chapter-rail-list > li > button { font-weight: 600; }
  .chapter-rail-list > li:has(.chapter-sublist [aria-current]) > button {
    color: var(--navy);
  }
}

@media (max-width: 1099px) {
  .chapter-trial-active .detail-tabs nav {
    position: relative;
    display: grid;
    grid-template-columns: repeat(3, minmax(0, 1fr));
    gap: 0;
  }

  .chapter-trial-active .detail-tabs nav::after {
    position: absolute;
    bottom: 0;
    left: 0;
    width: calc(100% / 3);
    height: 3px;
    border-radius: 3px 3px 0 0;
    background: var(--copper);
    content: "";
    transform: translateX(calc(100% * var(--chapter-index, 0)));
    transition: transform .36s cubic-bezier(.22, .76, .31, 1);
    pointer-events: none;
  }

  .chapter-trial-active .detail-tabs a {
    min-width: 0;
    border-bottom-color: transparent;
    text-align: center;
  }
}

@media (prefers-reduced-motion: reduce) {
  .chapter-rail-list::before,
  .chapter-rail-list::after,
  .chapter-hover-guide,
  .chapter-rail button,
  .chapter-trial-active .detail-tabs nav::after { transition: none; }
}