Two iPad 2 issues from screenshot:

1. Button text was left-aligned. On iOS 9 a <button> with display:flex
   ignores justify-content:center. Added text-align:center to .btn as a
   fallback (harmless when flex works).

2. Play symbol rendered as broken-glyph tofu. ▶ (U+25B6) gets emoji
   presentation which fails on iOS 9. Switched legacy play to ► (U+25BA),
   a text-presentation pointer in the same Geometric Shapes block as the
   ■ stop glyph that already renders fine. Canvas PLAY label now uses
   SYM.play too.

Modern browsers unaffected (still ▶ emoji, flex centering).

Co-Authored-By: Claude Sonnet 4.6 <noreply@anthropic.com>