Full Screen Motion

<style>
  /* The runtime auto-positions root children that carry data-start. The shared
     background deliberately has none, so it gets NO automatic layout and must
     size itself, or #bg is 0px tall and the tween paints nothing. */
  #bg.full-bleed {
    position: absolute;
    inset: 0;
  }
  .clip.transparent {
    background: transparent;
  }
</style>

<div id="root" data-composition-id="main" data-width="1920" data-height="1080" data-duration="20">
  <!-- Shared background — NOT a clip. Always visible. Driven by the timeline. -->
  <div id="bg" class="full-bleed"></div>

  <!-- Timed content layers — transparent backgrounds. -->
  <section
    id="scene1"
    class="clip transparent"
    data-start="0"
    data-duration="6"
    data-track-index="1"
  >
    <!-- content -->
  </section>
  <section
    id="scene2"
    class="clip transparent"
    data-start="6"
    data-duration="14"
    data-track-index="1"
  >
    <!-- content -->
  </section>
</div>

<script>
  const tl = gsap.timeline({ paused: true });

  // Drive the shared background from the seekable timeline.
  tl.to("#bg", { backgroundColor: "#0a1530", duration: 6, ease: "sine.inOut" }, 0);
  tl.to("#bg", { backgroundColor: "#1a0a30", duration: 14, ease: "sine.inOut" }, 6);

  // Scene-local animations stay transparent on top.
  tl.from("#scene1 h1", { y: 48, opacity: 0, duration: 0.6 }, 0.2);

  window.__timelines["main"] = tl;
</script>