#panels

A flex: 1 spacer takes all remaining height in a column, so every sibling after it starts at the container's bottom edge. Under overflow: hidden those trailing controls are laid out but never drawn: hover and onclick stay intact while zero pixels reach the screen. Put a spacer between two blocks that both fit, or bottom-anchor a group with margin-top: auto.

A Panel with overflow: scroll and real overflow content answers WantsDrag = true, and FindDragTarget walks up from the pointer to the first ancestor that claims the drag. That ancestor steals every press-and-drag from any slider, scrub bar, or knob inside it. Set CanDragScroll = false on the scroll container in OnTreeBuilt.

A dropdown paints cleanly over the block below it, and that block still eats every press. Paint order and hit order come from two different sums: render depth accumulates z-index down the tree, but hit-testing ranks siblings by SiblingIndex + ZIndex within each parent. An absolute menu that overhangs a later sibling looks perfect and is unclickable. Fix the ancestors, not the popup.