/* The flat-laid book: cover board, two pages, spine and flip layer. */

.stage {
  flex: 1;
  display: flex;
  align-items: center;
  justify-content: center;
  padding: 22px 50px;
  perspective: 2600px;
  overflow: hidden;
}

.book {
  /* Open spread of two A5 pages (148 x 210mm each), ratio kept exact via fitBook() in app.js */
  position: relative;
  display: flex;
  width: min(1440px, 100%);
  aspect-ratio: 148 / 105;
  max-height: 100%;
  padding: 18px;
  gap: 0;
  border-radius: var(--book-radius);
  background:
    linear-gradient(145deg, var(--cover), var(--cover-2));
  box-shadow:
    0 2px 0 var(--cover-stitch) inset,
    0 30px 60px -20px rgba(0, 0, 0, 0.75),
    0 0 0 1px var(--cover-edge);
  transform-style: preserve-3d;
}

.book::before {
  /* stitched border on the cover */
  content: "";
  position: absolute;
  inset: 8px;
  border: 1px dashed var(--cover-stitch);
  border-radius: calc(var(--book-radius) - 2px);
  pointer-events: none;
}

.page {
  position: relative;
  flex: 1 1 50%;
  min-width: 0;
  background: linear-gradient(180deg, var(--paper), var(--paper-2));
  box-shadow: 0 0 0 1px var(--paper-edge);
}

.page--left {
  border-radius: var(--page-radius) 0 0 var(--page-radius);
}

.page--right {
  border-radius: 0 var(--page-radius) var(--page-radius) 0;
}

.spine {
  width: 0;
  z-index: 2;
}

.page__inner {
  position: absolute;
  inset: 0;
  padding: calc(var(--pf, 1) * 22px) calc(var(--pf, 1) * 26px);
  overflow: hidden;
}

.page--left .page__inner {
  padding-right: calc(var(--pf, 1) * 38px);
}

.page--right .page__inner {
  padding-left: calc(var(--pf, 1) * 38px);
}

.page__folio,
.page__signature {
  position: absolute;
  bottom: 10px;
  font-size: 11px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--ink-faint);
}

.page--left .page__folio { left: 30px; }
.page--right .page__folio { right: 30px; }

.page--left .page__signature { right: 42px; }
.page--right .page__signature { left: 42px; }

.page__signature {
  font-family: var(--font-hand);
  font-size: 14px;
  letter-spacing: 0.04em;
  text-transform: none;
  color: var(--ink-soft);
}

.book.is-readonly .page__inner {
  filter: saturate(0.92);
}

/* ---- Edge tabs: flat leather index tabs ------------------------- */
.tab {
  position: absolute;
  top: 26%;
  display: flex;
  align-items: center;
  justify-content: center;
  width: 28px;
  height: 104px;
  padding: 0;
  cursor: pointer;
  color: var(--cover-ink);
  background: var(--cover-2);
  border: 1px solid var(--cover-edge);
  transition: background 0.15s ease, transform 0.15s ease;
  z-index: 7;
}

.tab::after {
  /* thin marker stripe along the outer edge */
  content: "";
  position: absolute;
  top: 14px;
  bottom: 14px;
  width: 2px;
  background: var(--cover-stitch);
}

.tab__label {
  display: block;
  writing-mode: vertical-rl;
  font-family: var(--font-head);
  font-size: 10px;
  letter-spacing: 0.26em;
  text-transform: uppercase;
  margin-bottom: -0.26em;
}

.tab:hover {
  background: var(--cover);
}

.tab--left {
  left: -28px;
  padding-left: 8px;
  border-right: none;
  border-radius: 10px 0 0 10px;
}

.tab--left::after {
  left: 6px;
}

.tab--left .tab__label {
  transform: rotate(180deg);
  margin-top: -0.26em;
  margin-bottom: 0;
}

.tab--left:hover {
  transform: translateX(-3px);
}

.tab--right {
  right: -28px;
  top: 48%;
  padding-right: 8px;
  border-left: none;
  border-radius: 0 10px 10px 0;
}

.tab--right::after {
  right: 6px;
}

.tab--right:hover {
  transform: translateX(3px);
}

.tab.is-active {
  color: var(--accent-ink);
  background: var(--accent);
  border-color: transparent;
}

.tab.is-active::after {
  background: rgba(0, 0, 0, 0.25);
}

.book.is-closed .tab {
  display: none;
}

/* ---- Cover: back board, spine, front board — page sized --------- */
.cover {
  position: absolute;
  inset: 18px;
  z-index: 9;
  display: flex;
  cursor: pointer;
  transform-origin: left center;
  animation: cover-close 480ms cubic-bezier(0.4, 0, 0.2, 1);
}

.cover[hidden] {
  display: none;
}

.cover__panel {
  position: relative;
  flex: 1 1 50%;
  min-width: 0;
  display: flex;
  flex-direction: column;
  align-items: center;
  justify-content: center;
  gap: 18px;
  background: var(--cover);
  box-shadow: inset 0 0 0 1px var(--cover-edge);
}

.cover__panel::before {
  content: "";
  position: absolute;
  inset: 14px;
  border: 1px dashed var(--cover-stitch);
  border-radius: 4px;
  pointer-events: none;
}

.cover__panel--back {
  border-radius: var(--page-radius) 0 0 var(--page-radius);
}

.cover__panel--front {
  border-radius: 0 var(--page-radius) var(--page-radius) 0;
}

.cover__spine {
  flex: none;
  width: 26px;
  background: var(--cover-2);
  box-shadow: inset 1px 0 0 var(--cover-edge), inset -1px 0 0 var(--cover-edge);
}

.cover__emboss {
  font-family: var(--font-head);
  font-size: 13px;
  letter-spacing: 0.4em;
  text-transform: uppercase;
  color: var(--cover-ink);
  opacity: 0.28;
}

.cover__plate {
  position: relative;
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 10px;
  padding: 34px 56px;
  color: var(--cover-ink);
  border: 1px solid var(--cover-stitch);
  border-radius: 4px;
  text-shadow: 0 1px 0 rgba(0, 0, 0, 0.45);
}

.cover__title {
  font-family: var(--font-head);
  font-size: 34px;
  letter-spacing: 0.14em;
  text-transform: uppercase;
}

.cover__rule {
  width: 110px;
  height: 1px;
  background: var(--cover-stitch);
}

.cover__owner {
  font: inherit;
  font-family: var(--font-hand);
  font-size: 22px;
  color: inherit;
  background: none;
  border: none;
  border-bottom: 1px dashed transparent;
  cursor: text;
  padding: 2px 6px;
}

.cover__owner:hover {
  border-bottom-color: var(--cover-stitch);
}

.cover__hint {
  position: absolute;
  bottom: 34px;
  font-size: 10px;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--cover-ink);
  opacity: 0.5;
}

@keyframes cover-close {
  from { transform: rotateY(-92deg); opacity: 0.2; }
  to { transform: rotateY(0deg); opacity: 1; }
}

/* ---- Page flip ------------------------------------------------ */
.flip-layer {
  position: absolute;
  inset: 18px;
  pointer-events: none;
  z-index: 6;
  perspective: 2600px;
}

.flip-layer:empty {
  display: none;
}

.flip-shim {
  position: absolute;
  top: 0;
  bottom: 0;
  width: 50%;
  overflow: hidden;
  background: linear-gradient(180deg, var(--paper), var(--paper-2));
}

.flip-shim--left { left: 0; }
.flip-shim--right { right: 0; }

.flip-sheet {
  position: absolute;
  top: 0;
  bottom: 0;
  width: 50%;
  transform-style: preserve-3d;
  will-change: transform;
}

.flip-sheet--forward {
  right: 0;
  transform-origin: left center;
  animation: flip-forward var(--flip-ms, 620ms) cubic-bezier(0.5, 0, 0.3, 1) forwards;
}

.flip-sheet--back {
  left: 0;
  transform-origin: right center;
  animation: flip-back var(--flip-ms, 620ms) cubic-bezier(0.5, 0, 0.3, 1) forwards;
}

.flip-face {
  position: absolute;
  inset: 0;
  overflow: hidden;
  backface-visibility: hidden;
  background: linear-gradient(180deg, var(--paper), var(--paper-2));
  box-shadow: 0 0 0 1px var(--paper-edge);
}

.flip-face--back {
  transform: rotateY(180deg);
}

.flip-face::after {
  /* curl shading that follows the turn */
  content: "";
  position: absolute;
  inset: 0;
  pointer-events: none;
  background: linear-gradient(to left, rgba(0, 0, 0, 0.22), transparent 45%);
  opacity: 0.9;
}

.flip-face--back::after {
  background: linear-gradient(to right, rgba(0, 0, 0, 0.22), transparent 45%);
}

@keyframes flip-forward {
  from { transform: rotateY(0deg); }
  to { transform: rotateY(-180deg); }
}

@keyframes flip-back {
  from { transform: rotateY(0deg); }
  to { transform: rotateY(180deg); }
}

@media (prefers-reduced-motion: reduce) {
  .flip-sheet--forward,
  .flip-sheet--back {
    animation-duration: 1ms;
  }
}

/* Narrow screens: flip through one leaf at a time instead of a two-page
   spread — cover, left page, right page, unplanned x2, back cover. */
.mobile-nav {
  display: none;
}

@media (max-width: 900px) {
  .flip-layer {
    display: none;
  }

  .tab {
    display: none;
  }

  .mobile-nav {
    flex: none;
    display: flex;
    align-items: center;
    justify-content: center;
    gap: 4px;
    padding: 8px 4px 2px;
  }

  .mobile-nav__btn {
    flex: none;
    width: 34px;
    height: 34px;
    display: grid;
    place-items: center;
    font-size: 18px;
    line-height: 1;
    color: var(--ui-fg);
    background: none;
    border: none;
    border-radius: 6px;
    cursor: pointer;
    transition: opacity 0.12s ease;
  }

  .mobile-nav__btn:active {
    opacity: 0.6;
  }

  .mobile-nav__btn:disabled {
    opacity: 0.25;
    cursor: default;
  }

  .mobile-nav__mid {
    flex: none;
    min-width: 0;
    display: flex;
    align-items: center;
  }

  .mobile-nav__label {
    display: none;
  }

  .mobile-nav__dots {
    display: flex;
    align-items: center;
    gap: 7px;
  }

  .mobile-nav__dot {
    flex: none;
    width: 6px;
    height: 6px;
    padding: 0;
    border: none;
    border-radius: 50%;
    background: var(--ui-border);
    cursor: pointer;
    transition: background 0.15s ease, transform 0.15s ease;
  }

  .mobile-nav__dot.is-active {
    background: var(--accent);
    transform: scale(1.4);
  }

  .stage {
    flex-direction: column;
    padding: 14px 18px;
  }

  .page {
    border-radius: var(--page-radius);
  }

  .page--left .page__inner,
  .page--right .page__inner {
    padding: calc(var(--pf, 1) * 20px);
    overflow: auto;
  }

  .cover__panel {
    flex: 1 1 100%;
  }

  /* Only the active leaf is rendered; every other leaf is pulled out of flow. */
  .stage[data-leaf] .page,
  .stage[data-leaf] .cover__panel {
    display: none;
  }

  .stage[data-leaf="left"] .page--left,
  .stage[data-leaf="unplanned-left"] .page--left {
    display: flex;
    flex: 1 1 100%;
  }

  .stage[data-leaf="right"] .page--right,
  .stage[data-leaf="unplanned-right"] .page--right {
    display: flex;
    flex: 1 1 100%;
  }

  .stage[data-leaf="cover-front"] .cover__panel--front,
  .stage[data-leaf="cover-back"] .cover__panel--back {
    display: flex;
  }

  .stage[data-leaf="cover-front"] .cover__spine,
  .stage[data-leaf="cover-back"] .cover__spine {
    display: none;
  }
}