.app {
  position: relative;
  width: 100vw;
  height: 100vh;
  overflow: hidden;
}

/* Header */
.header {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 64px;
  padding: 0 var(--scene-padding);
  display: flex;
  align-items: center;
  justify-content: space-between;
  z-index: 100;
  pointer-events: none;
}

.header__brand {
  display: flex;
  align-items: center;
  gap: 10px;
  pointer-events: auto;
  text-decoration: none;
  color: inherit;
}

.header__mark {
  width: 28px;
  height: 28px;
  object-fit: contain;
}

.header__name {
  font-family: var(--font-display);
  font-size: 18px;
  color: var(--navy-brand);
  letter-spacing: -0.01em;
}

.header__meta {
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.12em;
  text-transform: uppercase;
  color: var(--navy-deep);
  opacity: 0.5;
  pointer-events: auto;
}

/* Progress rail */
.progress {
  position: fixed;
  top: 0;
  left: 0;
  right: 0;
  height: 2px;
  background: transparent;
  z-index: 99;
}

.progress__fill {
  height: 100%;
  background: var(--blue-primary);
  width: 0%;
  transition: width 520ms var(--ease-out);
}

/* Scene viewport */
.scene {
  position: absolute;
  inset: 0;
  padding: 80px var(--scene-padding) 96px;
  display: flex;
  flex-direction: column;
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
  transition: opacity var(--dur-med) var(--ease-out);
}

.scene.is-active {
  opacity: 1;
  visibility: visible;
  pointer-events: auto;
}

.scene__header {
  display: flex;
  flex-direction: column;
  gap: 12px;
  margin-bottom: 36px;
  max-width: 780px;
}

.scene__number {
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.18em;
  text-transform: uppercase;
  color: var(--navy-deep);
  opacity: 0.45;
}

.scene__stage {
  flex: 1;
  position: relative;
  min-height: 0;
  min-width: 0;
  max-width: 100%;
}

/* Nav controls */
.nav {
  position: fixed;
  bottom: calc(24px + env(safe-area-inset-bottom, 0px));
  left: 50%;
  transform: translateX(-50%);
  display: flex;
  align-items: center;
  gap: 8px;
  padding: 8px;
  background: rgba(255, 255, 255, 0.9);
  backdrop-filter: saturate(180%) blur(12px);
  -webkit-backdrop-filter: saturate(180%) blur(12px);
  border: 1px solid var(--rule);
  border-radius: 999px;
  box-shadow: var(--shadow-2);
  z-index: 100;
}

.nav__btn {
  width: 36px;
  height: 36px;
  display: grid;
  place-items: center;
  border-radius: 50%;
  color: var(--navy-brand);
  transition: background var(--dur-fast) var(--ease-out), transform var(--dur-fast) var(--ease-out);
}

.nav__btn:hover {
  background: var(--canvas-soft);
  color: var(--blue-primary);
}

.nav__btn:active { transform: scale(0.94); }

.nav__btn:disabled {
  opacity: 0.3;
  cursor: not-allowed;
}

.nav__btn svg { width: 16px; height: 16px; }

.nav__dots {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 0 10px;
}

.nav__dot {
  width: 6px;
  height: 6px;
  border-radius: 50%;
  background: var(--rule);
  transition: background var(--dur-fast) var(--ease-out), transform var(--dur-fast) var(--ease-out);
  cursor: pointer;
  border: none;
  padding: 0;
}

.nav__dot:hover { background: var(--sky-interactive); }

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

.nav__counter {
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  color: var(--navy-deep);
  opacity: 0.6;
  padding: 0 10px;
  border-left: 1px solid var(--rule);
  border-right: 1px solid var(--rule);
  min-width: 56px;
  text-align: center;
}

/* Welcome overlay */
.welcome {
  position: fixed;
  inset: 0;
  z-index: 200;
  display: grid;
  place-items: center;
  background: var(--canvas-white);
  transition: opacity var(--dur-slow) var(--ease-out), visibility var(--dur-slow) var(--ease-out);
}

.welcome.is-gone {
  opacity: 0;
  visibility: hidden;
  pointer-events: none;
}

.welcome__inner {
  display: flex;
  flex-direction: column;
  align-items: center;
  gap: 32px;
  text-align: center;
  max-width: 540px;
  padding: 0 24px;
}

.welcome__wordmark {
  width: min(420px, 70vw);
  height: auto;
  opacity: 0;
  animation: fadeUp 900ms var(--ease-out) 200ms forwards;
}

.welcome__sub {
  font-family: var(--font-display);
  font-size: clamp(20px, 2vw, 26px);
  color: var(--navy-brand);
  opacity: 0;
  animation: fadeUp 900ms var(--ease-out) 500ms forwards;
  line-height: 1.35;
}

.welcome__meta {
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.2em;
  text-transform: uppercase;
  color: var(--navy-deep);
  opacity: 0;
  animation: fadeUp 900ms var(--ease-out) 800ms forwards;
}

.welcome__note {
  font-size: 12px;
  color: var(--navy-deep);
  opacity: 0;
  animation: fadeUp 900ms var(--ease-out) 950ms forwards;
  padding: 8px 14px;
  background: rgba(77, 168, 232, 0.08);
  border: 1px solid rgba(77, 168, 232, 0.22);
  border-radius: 8px;
  max-width: 320px;
  text-align: center;
}

.welcome__cta {
  display: inline-flex;
  align-items: center;
  gap: 10px;
  padding: 14px 28px;
  background: var(--navy-brand);
  color: white;
  border-radius: 999px;
  font-size: 14px;
  font-weight: 500;
  letter-spacing: 0.01em;
  transition: transform var(--dur-med) var(--ease-spring), background var(--dur-med) var(--ease-out), box-shadow var(--dur-med) var(--ease-out);
  opacity: 0;
  animation: fadeUp 900ms var(--ease-out) 1100ms forwards;
  box-shadow: var(--shadow-2);
}

.welcome__cta:hover {
  background: var(--blue-primary);
  transform: translateY(-2px);
  box-shadow: var(--shadow-hover);
}

.welcome__cta:active { transform: translateY(0); }

.welcome__cta svg {
  width: 14px;
  height: 14px;
  transition: transform var(--dur-fast) var(--ease-out);
}

.welcome__cta:hover svg { transform: translateX(3px); }

@keyframes fadeUp {
  from { opacity: 0; transform: translateY(12px); }
  to { opacity: 1; transform: translateY(0); }
}

/* Keyboard hint */
.khint {
  position: fixed;
  bottom: 24px;
  right: var(--scene-padding);
  display: flex;
  align-items: center;
  gap: 8px;
  font-family: var(--font-mono);
  font-size: 11px;
  letter-spacing: 0.08em;
  color: var(--navy-deep);
  opacity: 0.5;
  z-index: 90;
}

.khint kbd {
  font-family: var(--font-mono);
  font-size: 10px;
  padding: 2px 6px;
  background: var(--canvas-soft);
  border: 1px solid var(--rule);
  border-radius: 4px;
  color: var(--navy-brand);
}

@media (max-width: 768px) {
  .khint { display: none; }
  .header__meta { display: none; }
  .scene { padding: 64px 16px calc(96px + env(safe-area-inset-bottom, 0px)); }
  .scene__header { margin-bottom: 20px; gap: 8px; }
  .nav__dots { padding: 0 4px; gap: 4px; }
  .nav__counter { min-width: 46px; padding: 0 8px; font-size: 10px; }
}

@media (max-width: 600px) {
  h1 { font-size: clamp(28px, 6vw, 40px); }
  h2 { font-size: clamp(22px, 5vw, 30px); }
  .lede { font-size: 15px; }
  .nav__dot { width: 5px; height: 5px; }
  .nav__dot.is-active { transform: scale(1.3); }
  .nav { gap: 4px; padding: 6px; }
  .nav__btn { width: 32px; height: 32px; }
}