/* ============================================================================
   Cover frost-fall, motion law (nb_motion.css is the clock).
   Close / ice arriving = fade-in --nb-enter-ms (1500ms).
   Open / ice leaving = instant (no slide-away, no frost linger).
   Frost / sheen / blur stay painted while the sheet is visible.
   Reduced-motion / e-ink stay instant in notebook2.css + nb_motion.css.
   ============================================================================ */

@keyframes nb-cover-arrive {
  from { opacity: 0; }
  to { opacity: 1; }
}
@keyframes nb-cover-leave {
  from { opacity: 1; }
  to { opacity: 0; }
}

#nb-hero-glass.nb-hero-glass--unturn .nb-hero-page,
#nb-hero-glass.nb-hero-glass--turn .nb-hero-page {
  will-change: opacity;
}
#nb-hero-glass.nb-hero-glass--unturn .nb-hero-page {
  animation: nb-cover-arrive var(--nb-enter-ms, 1500ms) ease both;
  transform: none;
}
#nb-hero-glass.nb-hero-glass--turn .nb-hero-page {
  animation: none;
  opacity: 0;
  transform: none;
}

/* Honest ice during the arrive: do not kill blur or dim frost for a later settle. */
#nb-hero-glass.nb-hero-glass--unturn .nb-cover-frost,
#nb-hero-glass.nb-hero-glass--turn .nb-cover-frost {
  animation: none;
  opacity: 1;
  backdrop-filter: blur(10px) saturate(.7) brightness(.92);
  -webkit-backdrop-filter: blur(10px) saturate(.7) brightness(.92);
}
#nb-hero-glass.nb-hero-glass--unturn .nb-cover-sheen,
#nb-hero-glass.nb-hero-glass--turn .nb-cover-sheen {
  animation: none;
  opacity: .52;
}

/* After land: already ice. Quiet sheen drift only, no second frost-settle clock. */
#nb-hero-glass:not([hidden]):not(.nb-hero-glass--unturn):not(.nb-hero-glass--turn) .nb-cover-frost {
  animation: none;
  opacity: 1;
}
#nb-hero-glass:not([hidden]):not(.nb-hero-glass--unturn):not(.nb-hero-glass--turn) .nb-cover-sheen {
  animation: nb-cover-sheen-drift 22s ease-in-out infinite;
}