Browser UI Lock Test Pages

Tests for scrollbar-visibility detection. The feature locks UI gestures when neither html nor body has a visible vertical scrollbar.

Fullscreen App - Should lock (no scrollbar, 100% viewport)
Game Entry Example - Interactive demo with lock/unlock
Both Signals - Should lock (overflow hidden + no overflow content)
Normal Page - Should NOT lock (visible scrollbar)
Overscroll: none - Should NOT lock (has visible scrollbar despite overscroll-behavior)
Overscroll: contain - Should NOT lock (has visible scrollbar despite overscroll-behavior)
Overflow: hidden (body only) - Lock depends on html element scrollbar
SPA Style Change - Should detect late lock/unlock toggle