The global .hidden utility (display: none) also matches #sidebar.hidden,
so the collapsed sidebar was removed from layout before its width/opacity
transition could run, and opening and closing both snapped in one frame.
Keep the collapsed sidebar rendered and take it out of interaction once
closed: .sidebar.hidden stays display: flex, gains pointer-events: none,
and visibility: hidden that is transitioned so it only flips after the
collapse finishes (keeping the closed sidebar out of the tab order).
On desktop the icon rail now tucks under the sidebar and slides out as it
collapses, so the combined width eases instead of jumping by 48px when
the two swap. On mobile the drawer keeps its width while off so it slides
out as well as in, and switching it to the right edge before opening no
longer animates it across the screen. Transitions are disabled under
prefers-reduced-motion, and the auto-collapse restore measures the chat
width with the transition suppressed.
Re-record the computed-style snapshot baseline for the sidebar and icon
rail.
style-part-01..08 were arbitrary 6,000-line cuts, so the names said nothing
and a reader had no way to guess which file held a rule.
The original stylesheet turns out to be roughly area-grouped already, so
cutting where the content changes rather than every 6,000 lines produces
boundaries worth naming. Classifying every top-level rule by selector prefix
and smoothing over a 40-rule window gives 17 stable runs: agent-chat, compare,
memory, documents, admin-settings, skills, gallery, cookbook, tasks,
image-editor, email, notes, calendar, research.
The numeric prefix stays because load order is load-bearing, and it also
disambiguates the areas that appear twice: the original interleaves, and
merging non-adjacent blocks of the same area would reorder the cascade.
The names describe where a file sits, not a claim that it holds every rule for
that area or only rules for it. The header in each file says so, because that
is the misreading this naming invites.
Reconstruction was checked against lab's style.css before rewriting: identical
after whitespace normalisation, all 47,528 lines accounted for. The computed
style baseline still reproduces exactly.
Alexandre Teixeira