div.wtag-book {
  position: relative;
  padding: 0;
  display: block;
  overflow: hidden;
  width: 100%;
  height: 100%;
}

div.wtag-book.expand {
  position: absolute;
  left: 0;
  top: 0;
}

div.wtag-book > * {
  position: absolute;
  left: 0;
  top: 0;
  right: 0;
  bottom: 0;
  width: 100%;
  height: 100%;
  margin: 0;
}

div.wtag-book > *:not(.hidden) {
  display: block;
}

div.wtag-book > *.wtag-flex:not(.hidden) {
  display: flex;
}

div.wtag-book > *.hidden {
  display: none;
}