body {
  background: #f0f0f0;
  font-family: sans-serif;
}

#book {
  width: 420px;
  height: 600px;
  margin: 40px auto;
}

/* contenitore interno creato dalla libreria */
.stf__parent {
  box-shadow: 0 10px 30px rgba(0, 0, 0, 0.2);
}

/* singola pagina */
.page {
  background: white;
  color: #333;
  padding: 20px;
  box-sizing: border-box;
  border: 1px solid #e0e0e0;
}

/* effetto piega centrale */
.stf__block {
  box-shadow: inset 10px 0 20px -10px rgba(0, 0, 0, 0.25);
}

/* pagina sinistra */
.stf__block--left {
  border-right: 1px solid #ddd;
}

/* pagina destra */
.stf__block--right {
  border-left: 1px solid #ddd;
}

/* copertina */
.page.cover {
  background: #2c3e50;
  color: white;
  font-weight: bold;
  font-size: 24px;
  display: flex;
  align-items: center;
  justify-content: center;
}

  /* retro copertina */
  .page.cover.back {
    background: #34495e;
  }