quartz-research-note/quartz/components/styles/explorer.scss

button#explorer {
  background-color: transparent;
  border: none;
  text-align: left;
  cursor: pointer;
  padding: 0;
  color: var(--dark);
  display: flex;
  align-items: center;

  & h3 {
    font-size: 1rem;
    display: inline-block;
    margin: 0;
  }

  & .fold {
    margin-left: 0.5rem;
    transition: transform 0.3s ease;
    opacity: 0.8;
  }

  &.collapsed .fold {
    transform: rotateZ(-90deg);
  }
}

.folder-outer {
  display: grid;
  grid-template-rows: 0fr;
  transition: grid-template-rows 0.3s ease-in-out;
}

.folder-outer.open {
  grid-template-rows: 1fr;
}

.folder-outer > ul {
  overflow: hidden;
}

#explorer-content {
  list-style: none;
  overflow: hidden;
  max-height: none;
  transition: max-height 0.35s ease;
  margin-top: 0.5rem;

  &.collapsed > .overflow::after {
    opacity: 0;
  }

  & ul {
    list-style: none;
    margin: 0.08rem 0;
    padding: 0;
    transition:
      max-height 0.35s ease,
      transform 0.35s ease,
      opacity 0.2s ease;
    & div > li > a {
      color: var(--dark);
      opacity: 0.75;
      pointer-events: all;
    }
  }
}

svg {
  pointer-events: all;

  & > polyline {
    pointer-events: none;
  }
}

.folder-container {
  flex-direction: row;
  display: flex;
  align-items: center;
  user-select: none;

  & li > a {
    // other selector is more specific, needs important
    color: var(--secondary) !important;
    opacity: 1 !important;
    font-size: 1.05rem !important;
  }

  & li > a:hover {
    // other selector is more specific, needs important
    color: var(--tertiary) !important;
  }

  & li > button {
    color: var(--dark);
    background-color: transparent;
    border: none;
    text-align: left;
    cursor: pointer;
    padding-left: 0;
    padding-right: 0;
    display: flex;
    align-items: center;

    & h3 {
      font-size: 0.95rem;
      display: inline-block;
      color: var(--secondary);
      font-weight: 600;
      margin: 0;
      line-height: 1.5rem;
      font-weight: bold;
      pointer-events: none;
    }
  }
}

.folder-icon {
  margin-right: 5px;
  color: var(--secondary);
  cursor: pointer;
  transition: transform 0.3s ease;
  backface-visibility: visible;
}

div:has(> .folder-outer:not(.open)) > .folder-container > svg {
  transform: rotate(-90deg);
}

.folder-icon:hover {
  color: var(--tertiary);
}