Two user-reported issues fixed:
1. Slide layout broken in preview (content stuck to top, not centered)
Root cause: iframe CSS was forcing .slide { display:block !important }
which overrode base.css's .slide { display:flex; justify-content:center }
Fix: Do NOT override .slide or .deck styling in iframe. Let host CSS
(base.css + theme + scoped) handle flex centering, padding, etc.
Only override .is-active visibility and hide notes/chrome.
2. Users can now resize preview regions
- Horizontal splitter between current (left) and right column
- Vertical splitter between next preview (top) and notes (bottom)
- Splitters show blue hover state, drag updates flex sizes
- reScale() called on every drag frame to keep iframe 1:1 accurate
- Min sizes enforced (200px width, 80-100px height) to prevent collapse
Verified with headless Chrome: cover slide now correctly vertically
centered in the preview, matching audience view pixel-perfect.
0fc41be493