book.css

html {
  height: 100%;
  font-family: "Montserrat";
  display: grid;
  align-items: center;
  justify-items: center;
  --bg: #fcfcfc;
  --bg-panel: #ebebeb;
  --color-headings: #07f;
  --color-text: #333;
}
html[data-theme="dark"] {
  --bg: #333;
  --bg-panel: #434343;
  --color-headings: #3694ff;
  --color-text: #b5b5b5;
}
body {
  background-color: var(--bg);
}
.container {
  background-color: var(--bg-panel);
  margin: 5em;
  padding: 5em;
  border-radius: 15px;
  display: grid;
  grid-template-columns: 90% auto;
  grid-template-rows: auto auto;
  grid-template-areas: "title switch" "content content";
}
.container h1 {
  margin: 0;
  color: var(--color-headings);
}
.container p {
  color: var(--color-text);
  grid-area: content;
  font-size: 1.1em;
  line-height: 1.8em;
  margin-top: 2em;
}
input[type="checkbox"] {
  height: 0;
  width: 0;
  visibility: hidden;
}
label {
  cursor: pointer;
  text-indent: -9999px;
  width: 52px;
  height: 27px;
  background: grey;
  float: right;
  border-radius: 100px;
  position: relative;
}
label:after {
  content: "";
  position: absolute;
  top: 3px;
  left: 3px;
  width: 20px;
  height: 20px;
  background: #fff;
  border-radius: 90px;
  transition: 0.3s;
}
input:checked + label {
  background: var(--color-headings);
}
input:checked + label:after {
  left: calc(100% - 5px);
  transform: translateX(-100%);
}
label:active:after {
  width: 45px;
}
html.transition,
html.transition *,
html.transition *:before,
html.transition *:after {
  transition: all 750ms !important;
  transition-delay: 0 !important;
}