html, body {
  margin: 0;
  width: 100vw;
  height: 100vh;
  font-family: Arial, sans-serif;
  background: url('../images/wood.jpg') center center/cover no-repeat;
  overflow: hidden;
}
.preloader {
  position: fixed;
  inset: 0;
  width: 100vw;
  height: 100vh;
  z-index: 1000;
  display: flex;
  justify-content: center;
  align-items: center;
  background: transparent;
  transition: opacity .5s;
}
.preloader img {
  max-width: 70vw;
  max-height: 60vh;
  border-radius: 16px;
  box-shadow: 0 4px 28px rgba(0,0,0,0.29);
  display: block;
  outline: none;
  border: none;
  background: none;
}
.flipbook-section {
  width: 100vw;
  height: 100vh;
  display: flex;
  flex-direction: column;
  justify-content: center;
  align-items: center;
}
.menu-area {
  width: 100vw;
  height: calc(100vh - 70px);
  position: relative;
  display: flex;
  justify-content: center;
  align-items: center;
  overflow: hidden;
}
.flipbook-page {
  position: absolute;
  top: 50%;
  left: 50%;
  width: min(92vw, calc((100vh - 70px) * 0.75));
  height: min(calc(100vh - 70px), calc(92vw * 1.3333));
  background-size: contain;
  background-repeat: no-repeat;
  background-position: center center;
  box-shadow: 0 8px 48px 0 rgba(0,0,0,0.18);
  border-radius: 14px;
  transform: translate(-50%, -50%);
  backface-visibility: hidden;
  transition: transform 0.8s cubic-bezier(0.49, 1.37, 0.66, 0.93);
  z-index: 2;
}
.flipbook-page.flipping.flip-left {
  transform: translate(-50%, -50%) rotateY(-100deg);
}
.flipbook-page.flipping.flip-right {
  transform: translate(-50%, -50%) rotateY(100deg);
}
.menu-btn {
  background: rgba(0,0,0,0.28);
  border: 0;
  color: #fffbe8;
  border-radius: 50%;
  width: 56px;
  height: 56px;
  font-size: 2.1rem;
  margin: 0 22px;
  display: flex;
  align-items: center;
  justify-content: center;
  cursor: pointer;
  box-shadow: 0 2px 12px 0 rgba(0,0,0,0.17);
  user-select: none;
  transition: background 0.2s;
  position: relative;
  z-index: 10;
}
.menu-btn:hover {
  background: #f1c564;
  color: #7c5535;
}
.menu-pager {
  margin-top: 10px;
  padding: 10px 24px;
  background: rgba(0,0,0,0.33);
  color: #fffbe8;
  border-radius: 16px;
  font-size: 1.2rem;
  box-shadow: 0 2px 12px 0 rgba(0,0,0,0.17);
  user-select: none;
}
.arrow-left {
  position: absolute;
  left: 24px;
  top: 50%;
  transform: translateY(-50%);
}
.arrow-right {
  position: absolute;
  right: 24px;
  top: 50%;
  transform: translateY(-50%);
}
@media (max-width:700px) {
  .flipbook-page {
    width: min(96vw, calc((100vh - 70px) * 0.72));
    height: min(calc(100vh - 70px), calc(96vw * 1.32));
  }
  .menu-btn {
    width: 40px;
    height: 40px;
    font-size: 1.4rem;
    margin: 0 6px;
  }
  .menu-pager {
    font-size: 1rem;
    padding: 7px 13px;
  }
}