/*****************************************************
SCROLLSTORY SEQUENCE

Full-width photographs with passages that move through the page's normal flow.
Each photograph stays in view until its passage clears the top. Scroll mode
then lets the image leave; fade mode holds the frame and changes its layers.
Both use ordinary page scrolling, with no wheel or touch input handling.

Loads:    every page
Used by:  scrollstory/sequence.html
Needs:    base.css tokens and container grid; home.css --home-measure
Not here: the contained source editor (story-demo.css), or the older background
          components (backgrounds.css)
*****************************************************/

.container > .story-sequence {
  grid-column: full;
  margin-block: var(--spacing-lg);
}

.story-sequence-intro {
  max-width: var(--home-measure);
  margin-inline: auto;
  padding: 0 var(--spacing-md) var(--spacing-md);
}
.story-sequence-heading { margin: 0; }
.story-sequence-intro p { margin: var(--spacing-sm) 0 0; }
.story-sequence-scenes { position: relative; }

.story-sequence-scene {
  display: grid;
  grid-template-columns: minmax(0, 1fr);
  align-items: start;
}

/* Sharing a grid cell gives the text a real place in the document while the
   photograph sticks within this scene. Neither layer captures scrolling. */
.story-sequence-image {
  grid-area: 1 / 1;
  position: sticky;
  top: 0;
  height: var(--story-sequence-view-height);
}
.story-sequence-image img {
  display: block;
  width: 100%;
  height: 100%;
  object-fit: cover;
}

.story-sequence-passage {
  grid-area: 1 / 1;
  position: relative;
  z-index: 1;
  /* One screen above and below the card is deliberate. When the next image
     first enters at the bottom, the whole current card has cleared the top. */
  padding: var(--story-sequence-view-height) max(var(--spacing-md), calc((100% - var(--home-measure)) / 2));
}
.story-sequence-card {
  max-width: 28rem;
  padding: var(--spacing-md);
  color: var(--text-body);
  background: var(--bg-card);
  border-radius: var(--radius-sm);
  box-shadow: var(--shadow-md);
}
.story-sequence-card :is(h1, h2, h3, h4, h5, h6) {
  margin: 0 0 var(--spacing-sm);
  font-family: var(--font-serif);
  color: inherit;
}
.story-sequence-card p { margin: 0 0 var(--spacing-sm); text-align: left; }
.story-sequence-card > :last-child { margin-bottom: 0; }

.story-sequence-backdrop {
  position: sticky;
  top: 0;
  height: var(--story-sequence-view-height);
  margin-bottom: calc(-1 * var(--story-sequence-view-height));
}
.story-sequence-backdrop[hidden] { display: none; }
.story-sequence-layer {
  position: absolute;
  inset: 0;
  width: 100%;
  height: 100%;
  object-fit: cover;
  opacity: 0;
  transition: opacity var(--transition-slow);
}
.story-sequence-layer--active { opacity: 1; }
.story-sequence--fade-ready .story-sequence-scene { display: block; position: relative; }
/* Successive cards enter as the previous one clears; only the final card
   needs a full trailing screen before the shared frame can leave. */
.story-sequence--fade-ready .story-sequence-scene:not(:last-child) .story-sequence-passage {
  padding-bottom: 0;
}
/* Keep each original photo in reading order for assistive technology. The
   visible shared backdrop is decorative and excluded from that reading order. */
.story-sequence--fade-ready .story-sequence-image {
  position: absolute;
  width: 1px;
  height: 1px;
  clip-path: inset(50%);
  overflow: hidden;
}

@supports (height: 100svh) {
  .story-sequence {
    --story-sequence-view-height: 100svh;
  }
}

@media (max-width: 600px) {
  .story-sequence-intro { padding-inline: var(--spacing-sm); }
  .story-sequence-passage { padding-inline: var(--spacing-sm); }
}

@media print, (prefers-reduced-motion: reduce) {
  .story-sequence .story-sequence-scene { display: block; }
  .story-sequence .story-sequence-image {
    position: static;
    width: auto;
    height: auto;
    clip-path: none;
    overflow: visible;
  }
  .story-sequence-backdrop { display: none; }
  .story-sequence-image img { height: auto; }
  .story-sequence-passage,
  .story-sequence.story-sequence--fade-ready .story-sequence-scene .story-sequence-passage {
    padding-block: var(--spacing-lg);
  }
  .story-sequence-card { box-shadow: none; }
}