.book-summary li.chapter.has-children {
  position: relative;
}

.book-summary li.chapter.has-children > .honkit-collapse-toggle {
  position: absolute;
  top: 7px;
  right: 8px;
  z-index: 2;
  width: 24px;
  height: 24px;
  padding: 0;
  border: 0;
  border-radius: 4px;
  color: #7f8c8d;
  background: transparent;
  cursor: pointer;
  font-size: 16px;
  line-height: 24px;
}

.book-summary li.chapter.has-children > .honkit-collapse-toggle:hover,
.book-summary li.chapter.has-children > .honkit-collapse-toggle:focus {
  color: #008cff;
  background: rgba(0, 140, 255, 0.08);
  outline: none;
}

.book-summary li.chapter.has-children > .honkit-collapse-toggle::before {
  content: "›";
  display: inline-block;
  transform: rotate(0deg);
  transition: transform 120ms ease;
}

.book-summary li.chapter.has-children.is-expanded > .honkit-collapse-toggle::before {
  transform: rotate(90deg);
}

.book-summary li.chapter > ul.articles {
  display: none !important;
}

.book-summary li.chapter.has-children.is-expanded > ul.articles {
  display: block !important;
}