Root cause: Tailwind's `duration-100` utility sets the literal CSS
`transition-duration` property (it's meant for transitions, not
animations). Since `transition-property`'s initial value is `all` and
nothing overrode it, every element using `duration-100` in its
Transition enter/leave-active-class picked up an unintended
`transition: all 100ms`. For SelectContent, whose `top`/`left` are set
via inline style from usePopoverPosition, this meant the popover's
real computed position (set synchronously on mount) got smoothly
interpolated from the reactive object's initial {top:0,left:0} default
-- visibly flying in from the top-left corner of the viewport before
landing in place.
Fix: use tw-animate-css's dedicated `animation-duration-*` utility
instead, which sets `animation-duration`/`--tw-animation-duration`
without ever touching `transition-property`/`transition-duration`.
Confirmed via computed-style inspection in headless Chromium that
transitionDuration is now 0s while the intended enter/exit keyframe
animation still runs for 100ms. Applied everywhere `duration-100` was
used for this pattern (DialogContent, DialogOverlay,
DialogScrollContent, SelectContent).
Matthew L McPeak
a2685c6920