/* ─── Variables ─────────────────────────────────────────── */
:root {
  --accent: #3b82f6;
  --text: #eaeaea;
  --panel-bg: #0f0f0f;
  --anim-dur: 0.65s;
  --anim-ease: cubic-bezier(0.645, 0.045, 0.355, 1.000);
  --safe-bottom: env(safe-area-inset-bottom, 0px);
  --bar-h: 60px;
}

/* ─── Reset ─────────────────────────────────────────────── */
*, *::before, *::after {
  -webkit-box-sizing: border-box;
  box-sizing: border-box;
  margin: 0; padding: 0;
}

html {
  -webkit-text-size-adjust: 100%;
  -ms-text-size-adjust: 100%;
}

html, body {
  height: 100%; width: 100%;
  overflow: hidden;
  background: #000;
  color: #eaeaea;
  color: var(--text);
  font-family: -apple-system, BlinkMacSystemFont, "Segoe UI", Roboto, Helvetica, Arial, sans-serif;
  overscroll-behavior: none;
  -ms-scroll-chaining: none;
  /* Prevent iOS long-press text selection */
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
}

/* ─── Book Stage ─────────────────────────────────────────── */
.book-stage {
  position: fixed;
  top: 0; left: 0; right: 0; bottom: 0;
  background: #000;
  /* Mobile-optimised perspective — smaller value = more dramatic curl on narrow screens */
  -webkit-perspective: 1200px;
  perspective: 1200px;
  overflow: hidden;
  /* CRITICAL: prevent browser scroll/zoom from eating touch events */
  touch-action: none;
}

/* Wider screens get deeper perspective for subtler effect */
@media (min-width: 769px) {
  .book-stage {
    -webkit-perspective: 2000px;
    perspective: 2000px;
  }
}

.book-layer {
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-align: center;
  -ms-flex-align: center;
  align-items: center;
  -webkit-box-pack: center;
  -ms-flex-pack: center;
  justify-content: center;
  /* Force GPU compositing layer on both layers */
  -webkit-transform: translateZ(0);
  transform: translateZ(0);
}

/* Back layer — destination slide, revealed during flip */
#backLayer { z-index: 1; }

/* Shadow sweep on back layer as the flipping page uncovers it */
#backLayer::after {
  content: '';
  position: absolute;
  top: 0; left: 0; right: 0; bottom: 0;
  pointer-events: none;
  opacity: 0;
}

#backLayer.reveal-fwd::after {
  background: -webkit-linear-gradient(left, rgba(0,0,0,0.85) 0%, rgba(0,0,0,0.3) 30%, transparent 60%);
  background: linear-gradient(to right, rgba(0,0,0,0.85) 0%, rgba(0,0,0,0.3) 30%, transparent 60%);
  -webkit-animation: shadowFade var(--anim-dur) var(--anim-ease) forwards;
  animation: shadowFade var(--anim-dur) var(--anim-ease) forwards;
}

#backLayer.reveal-bwd::after {
  background: -webkit-linear-gradient(right, rgba(0,0,0,0.85) 0%, rgba(0,0,0,0.3) 30%, transparent 60%);
  background: linear-gradient(to left, rgba(0,0,0,0.85) 0%, rgba(0,0,0,0.3) 30%, transparent 60%);
  -webkit-animation: shadowFade var(--anim-dur) var(--anim-ease) forwards;
  animation: shadowFade var(--anim-dur) var(--anim-ease) forwards;
}

@-webkit-keyframes shadowFade {
  0%   { opacity: 1; }
  100% { opacity: 0; }
}
@keyframes shadowFade {
  0%   { opacity: 1; }
  100% { opacity: 0; }
}

/* Front layer — current slide, animates away like a book page */
#frontLayer {
  z-index: 2;
  -webkit-backface-visibility: hidden;
  backface-visibility: hidden;
  /* Pre-allocate GPU compositing layer for smooth animation */
  will-change: transform;
  -webkit-transform: translateZ(0);
  transform: translateZ(0);
}

/* ── Forward: page curls left (next slide) ── */
#frontLayer.flip-fwd {
  -webkit-transform-origin: left center;
  -ms-transform-origin: left center;
  transform-origin: left center;
  -webkit-animation: flipFwd var(--anim-dur) var(--anim-ease) forwards;
  animation: flipFwd var(--anim-dur) var(--anim-ease) forwards;
}
@-webkit-keyframes flipFwd {
  0%   { -webkit-transform: rotateY(0deg); }
  100% { -webkit-transform: rotateY(-180deg); }
}
@keyframes flipFwd {
  0%   { transform: rotateY(0deg); }
  100% { transform: rotateY(-180deg); }
}

/* ── Backward: page curls right (previous slide) ── */
#frontLayer.flip-bwd {
  -webkit-transform-origin: right center;
  -ms-transform-origin: right center;
  transform-origin: right center;
  -webkit-animation: flipBwd var(--anim-dur) var(--anim-ease) forwards;
  animation: flipBwd var(--anim-dur) var(--anim-ease) forwards;
}
@-webkit-keyframes flipBwd {
  0%   { -webkit-transform: rotateY(0deg); }
  100% { -webkit-transform: rotateY(180deg); }
}
@keyframes flipBwd {
  0%   { transform: rotateY(0deg); }
  100% { transform: rotateY(180deg); }
}

/* Slide images */
.book-layer img {
  display: block;
  max-width: 100%;
  /* Account for bottom bar height AND safe area inset on notched phones */
  max-height: calc(100% - var(--bar-h) - var(--safe-bottom));
  width: auto;
  height: auto;
  -o-object-fit: contain;
  object-fit: contain;
  -webkit-box-shadow: 0 12px 80px rgba(0,0,0,0.9);
  box-shadow: 0 12px 80px rgba(0,0,0,0.9);
  pointer-events: none;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
  /* Prevent drag ghost on desktop */
  -webkit-drag: none;
}

/* ─── Nav Arrows ─────────────────────────────────────────── */
.nav-arrow {
  position: fixed;
  top: 50%;
  -webkit-transform: translateY(-50%);
  -ms-transform: translateY(-50%);
  transform: translateY(-50%);
  z-index: 40;
  background: rgba(0,0,0,0.3);
  border: 1px solid rgba(255,255,255,0.1);
  color: #fff;
  width: 52px;
  height: 110px;
  cursor: pointer;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-align: center;
  -ms-flex-align: center;
  align-items: center;
  -webkit-box-pack: center;
  -ms-flex-pack: center;
  justify-content: center;
  -webkit-backdrop-filter: blur(8px);
  backdrop-filter: blur(8px);
  /* Prevent double-tap zoom; allow tap to work cleanly */
  touch-action: manipulation;
  -webkit-tap-highlight-color: transparent;
  -webkit-transition: background 0.2s, opacity 0.35s;
  transition: background 0.2s, opacity 0.35s;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
}
.nav-prev {
  left: 0;
  -webkit-border-radius: 0 12px 12px 0;
  border-radius: 0 12px 12px 0;
  border-left: none;
}
.nav-next {
  right: 0;
  -webkit-border-radius: 12px 0 0 12px;
  border-radius: 12px 0 0 12px;
  border-right: none;
}
.nav-arrow:hover, .nav-arrow:focus { background: rgba(0,0,0,0.72); outline: none; }
.nav-arrow:active { background: rgba(59,130,246,0.45); }
.nav-arrow:disabled { opacity: 0.15 !important; cursor: default; pointer-events: none; }
.nav-arrow svg { width: 26px; height: 26px; }

/* ─── Bottom Bar ─────────────────────────────────────────── */
.bottom-bar {
  position: fixed;
  bottom: 0; left: 0; right: 0;
  z-index: 40;
  padding-bottom: env(safe-area-inset-bottom, 0px);
  -webkit-transition: opacity 0.5s ease;
  transition: opacity 0.5s ease;
}
.progress-track {
  height: 3px;
  background: rgba(255,255,255,0.1);
  overflow: hidden;
}
.progress-fill {
  height: 100%;
  background: #3b82f6;
  background: var(--accent);
  width: 0%;
  -webkit-transition: width 0.38s ease;
  transition: width 0.38s ease;
}
.bottom-controls {
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-align: center;
  -ms-flex-align: center;
  align-items: center;
  -webkit-box-pack: justify;
  -ms-flex-pack: justify;
  justify-content: space-between;
  padding: 10px 18px 14px;
  background: -webkit-linear-gradient(top, transparent, rgba(0,0,0,0.9));
  background: linear-gradient(to bottom, transparent, rgba(0,0,0,0.9));
}

/* ─── Control Buttons ────────────────────────────────────── */
.ctrl-btn {
  background: transparent;
  border: none;
  color: #eaeaea;
  color: var(--text);
  cursor: pointer;
  min-width: 44px;
  min-height: 44px;
  display: -webkit-inline-box;
  display: -ms-inline-flexbox;
  display: inline-flex;
  -webkit-box-align: center;
  -ms-flex-align: center;
  align-items: center;
  -webkit-box-pack: center;
  -ms-flex-pack: center;
  justify-content: center;
  -webkit-border-radius: 8px;
  border-radius: 8px;
  touch-action: manipulation;
  -webkit-tap-highlight-color: transparent;
  opacity: 0.75;
  -webkit-transition: opacity 0.2s, background 0.2s;
  transition: opacity 0.2s, background 0.2s;
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
}
.ctrl-btn:hover, .ctrl-btn:focus { opacity: 1; background: rgba(255,255,255,0.09); outline: none; }
.ctrl-btn:active { opacity: 1; background: rgba(59,130,246,0.35); }
.ctrl-btn svg { width: 20px; height: 20px; }

.counter {
  font-size: 14px;
  letter-spacing: 0.06em;
  color: rgba(255,255,255,0.75);
  -webkit-user-select: none;
  -moz-user-select: none;
  -ms-user-select: none;
  user-select: none;
}
.counter .sep { color: rgba(255,255,255,0.3); }

/* ─── Auto-hide (desktop / mouse devices only) ───────────── */
.nav-arrow,
.bottom-bar {
  -webkit-transition: opacity 0.5s ease;
  transition: opacity 0.5s ease;
}
body.ui-hidden .nav-arrow,
body.ui-hidden .bottom-bar {
  opacity: 0;
  pointer-events: none;
}

/* OVERRIDE: never auto-hide on touch/mobile devices */
@media (hover: none) and (pointer: coarse) {
  body.ui-hidden .nav-arrow,
  body.ui-hidden .bottom-bar {
    opacity: 1;
    pointer-events: auto;
  }
  /* Keep arrows visible at resting opacity on touch screens */
  .nav-arrow { opacity: 0.65; }
  .nav-arrow:active { opacity: 1; }
}

/* ─── Swipe hint (shown once on first mobile load) ──────── */
.swipe-hint {
  position: fixed;
  bottom: 80px;
  left: 50%;
  -webkit-transform: translateX(-50%);
  -ms-transform: translateX(-50%);
  transform: translateX(-50%);
  background: rgba(0,0,0,0.72);
  color: rgba(255,255,255,0.9);
  padding: 9px 18px;
  -webkit-border-radius: 20px;
  border-radius: 20px;
  font-size: 13px;
  white-space: nowrap;
  z-index: 60;
  pointer-events: none;
  -webkit-animation: hintAnim 3s ease-in-out forwards;
  animation: hintAnim 3s ease-in-out forwards;
}
.swipe-hint::before {
  content: '← ';
  opacity: 0.6;
}
.swipe-hint::after {
  content: ' →';
  opacity: 0.6;
}
@-webkit-keyframes hintAnim {
  0%   { opacity: 0; -webkit-transform: translateX(-50%) translateY(6px); }
  15%  { opacity: 1; -webkit-transform: translateX(-50%) translateY(0); }
  70%  { opacity: 1; }
  100% { opacity: 0; }
}
@keyframes hintAnim {
  0%   { opacity: 0; transform: translateX(-50%) translateY(6px); }
  15%  { opacity: 1; transform: translateX(-50%) translateY(0); }
  70%  { opacity: 1; }
  100% { opacity: 0; }
}

/* ─── Portrait hint on small phones ─────────────────────── */
.portrait-hint {
  position: fixed;
  top: 12px;
  left: 50%;
  -webkit-transform: translateX(-50%);
  -ms-transform: translateX(-50%);
  transform: translateX(-50%);
  background: rgba(0,0,0,0.65);
  color: rgba(255,255,255,0.75);
  padding: 6px 14px;
  -webkit-border-radius: 14px;
  border-radius: 14px;
  font-size: 12px;
  white-space: nowrap;
  z-index: 60;
  pointer-events: none;
  -webkit-animation: hintAnim 4s ease-in-out forwards;
  animation: hintAnim 4s ease-in-out forwards;
}

/* ─── Thumbnail Panel ────────────────────────────────────── */
.panel-backdrop {
  display: none;
  position: fixed;
  top: 0; left: 0; right: 0; bottom: 0;
  background: rgba(0,0,0,0.72);
  -webkit-backdrop-filter: blur(4px);
  backdrop-filter: blur(4px);
  z-index: 98;
}
.panel-backdrop.visible { display: block; }

.thumb-panel {
  position: fixed;
  left: 0; right: 0; bottom: 0;
  z-index: 99;
  background: #0f0f0f;
  background: var(--panel-bg);
  border-top: 1px solid rgba(255,255,255,0.07);
  -webkit-border-radius: 22px 22px 0 0;
  border-radius: 22px 22px 0 0;
  max-height: 74vh;
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-orient: vertical;
  -webkit-box-direction: normal;
  -ms-flex-direction: column;
  flex-direction: column;
  -webkit-transform: translateY(100%);
  -ms-transform: translateY(100%);
  transform: translateY(100%);
  -webkit-transition: -webkit-transform 0.4s cubic-bezier(0.32, 0.72, 0, 1);
  transition: transform 0.4s cubic-bezier(0.32, 0.72, 0, 1);
  padding-bottom: env(safe-area-inset-bottom, 0px);
}
.thumb-panel.open {
  -webkit-transform: translateY(0);
  -ms-transform: translateY(0);
  transform: translateY(0);
}

.panel-handle {
  width: 40px; height: 4px;
  background: rgba(255,255,255,0.2);
  -webkit-border-radius: 2px;
  border-radius: 2px;
  margin: 12px auto 0;
  -ms-flex-negative: 0;
  flex-shrink: 0;
}

.thumb-panel-header {
  display: -webkit-box;
  display: -ms-flexbox;
  display: flex;
  -webkit-box-align: center;
  -ms-flex-align: center;
  align-items: center;
  -webkit-box-pack: justify;
  -ms-flex-pack: justify;
  justify-content: space-between;
  padding: 10px 20px 12px;
  border-bottom: 1px solid rgba(255,255,255,0.05);
  -ms-flex-negative: 0;
  flex-shrink: 0;
}
.thumb-panel-title {
  font-size: 12px;
  font-weight: 600;
  letter-spacing: 0.08em;
  text-transform: uppercase;
  color: rgba(255,255,255,0.4);
}
.thumb-close-btn { opacity: 0.6; font-size: 15px; }

.thumb-grid {
  overflow-y: auto;
  -webkit-overflow-scrolling: touch;
  overscroll-behavior: contain;
  padding: 12px;
  display: -ms-grid;
  display: grid;
  -ms-grid-columns: 1fr 8px 1fr 8px 1fr 8px 1fr;
  grid-template-columns: repeat(4, 1fr);
  gap: 8px;
  /* Allow vertical scroll even though parent has touch-action:none */
  touch-action: pan-y;
}

/* Thumbnail cell — padding-top aspect ratio trick */
.thumb-cell {
  position: relative;
  padding-top: 69.2%; /* 1125 / 1626 */
  overflow: hidden;
  -webkit-border-radius: 7px;
  border-radius: 7px;
  cursor: pointer;
  border: 2px solid transparent;
  background: #1c1c1c;
  touch-action: manipulation;
  -webkit-tap-highlight-color: transparent;
  -webkit-transition: border-color 0.15s, -webkit-transform 0.15s;
  transition: border-color 0.15s, transform 0.15s;
}
.thumb-cell:hover { -webkit-transform: scale(1.04); transform: scale(1.04); }
.thumb-cell.active { border-color: #3b82f6; border-color: var(--accent); }
.thumb-cell:focus { outline: 2px solid #3b82f6; outline: 2px solid var(--accent); outline-offset: 2px; }

.thumb-cell img {
  position: absolute;
  top: 0; left: 0;
  width: 100%; height: 100%;
  display: block;
  -o-object-fit: cover;
  object-fit: cover;
  pointer-events: none;
}
.thumb-badge {
  position: absolute;
  bottom: 4px; right: 5px;
  font-size: 9px;
  color: rgba(255,255,255,0.75);
  background: rgba(0,0,0,0.6);
  padding: 1px 4px;
  -webkit-border-radius: 3px;
  border-radius: 3px;
  line-height: 1.5;
  pointer-events: none;
}

/* ─── Responsive ─────────────────────────────────────────── */
@media (min-width: 600px) {
  .thumb-grid {
    -ms-grid-columns: 1fr 8px 1fr 8px 1fr 8px 1fr 8px 1fr 8px 1fr;
    grid-template-columns: repeat(6, 1fr);
  }
}
@media (min-width: 1024px) {
  .thumb-grid { grid-template-columns: repeat(8, 1fr); }
  .nav-arrow { width: 62px; height: 130px; }
}

/* Small phones */
@media (max-width: 480px) {
  .thumb-grid {
    -ms-grid-columns: 1fr 6px 1fr 6px 1fr;
    grid-template-columns: repeat(3, 1fr);
    gap: 6px; padding: 10px;
  }
  .nav-arrow { width: 46px; height: 90px; }
  .nav-arrow svg { width: 22px; height: 22px; }
  .counter { font-size: 13px; }
}

/* Landscape phones */
@media (max-height: 500px) and (orientation: landscape) {
  :root { --bar-h: 50px; }
  .nav-arrow { height: 64px; width: 42px; }
  .bottom-controls { padding: 6px 16px 8px; }
}

/* ─── Mobile portrait: move nav arrows above the slide ───── */
@media (max-width: 768px) and (orientation: portrait) {
  .nav-arrow {
    /* unset the vertical-centre positioning */
    top: calc(env(safe-area-inset-top, 0px) + 12px);
    bottom: auto;
    -webkit-transform: none;
    -ms-transform: none;
    transform: none;
    /* circular shape */
    width: 48px;
    height: 48px;
    -webkit-border-radius: 50%;
    border-radius: 50%;
    border: 1px solid rgba(255,255,255,0.18);
  }
  /* restore left/right borders that were removed on the side-arrow style */
  .nav-prev {
    left: 16px;
    -webkit-border-radius: 50%;
    border-radius: 50%;
    border-left: 1px solid rgba(255,255,255,0.18);
  }
  .nav-next {
    right: 16px;
    -webkit-border-radius: 50%;
    border-radius: 50%;
    border-right: 1px solid rgba(255,255,255,0.18);
  }
  .nav-arrow svg {
    width: 22px;
    height: 22px;
  }
  /* Push slide image down so it clears the top arrows */
  .book-layer {
    -webkit-box-align: center;
    -ms-flex-align: center;
    align-items: center;
    padding-top: calc(env(safe-area-inset-top, 0px) + 72px);
    padding-bottom: calc(var(--bar-h, 60px) + env(safe-area-inset-bottom, 0px));
  }
  .book-layer img {
    max-height: 100%;
  }
}