Marker labels invisible on Safari / Firefox (no CSS Anchor Positioning)

[Yeom-JinHo]

v2's bindable markers rely on CSS Anchor Positioning, which only Chromium ships today. On Safari, Firefox, and every iOS browser (Chrome, Edge, Firefox on iOS all use WebKit per App Store policy), anchor() is silently ignored and labels collapse — they have no way to find the marker's screen position.

This isn't a "use a different browser" workaround on iOS, since there isn't one.

Desktop Chrome (works)

iOS Chrome / Safari (broken)

Proposal

cobe already computes each marker's screen position and writes it to an invisible anchor div as style.left/top. Publishing the same values as global CSS variables would let users author a one-line

fallback:

.label {
  /* Chromium */
  position-anchor: --cobe-sf;
  bottom: anchor(top); left: anchor(center);

  /* Safari / Firefox / iOS */
  @supports not (anchor-name: --x) {
    left: var(--cobe-sf-x); top: var(--cobe-sf-y);
    transform: translate(-50%, -100%);
  }
}

~6 lines of runtime change, additive, no API/type changes.
Happy to send a PR if the direction looks good.