The last commit set the sentence moving, and on a wide window it moved the
wrong way: two copies rode the track and the track slid half its own width, so
the loop was seamless because the second copy arrived exactly where the first
had left. That is the right shape for a marquee and the wrong one for this
sentence. A seamless loop means the string never enters the screen and never
leaves it — the pair is already in flight at t=0 and the seam hides the moment
one copy hands over to the other. At 1440 with a 713px string both copies fit
in the window, so what the visitor saw was two identical sentences standing
side by side, walking, and neither of them had ever come from anywhere.
The ask is one sentence at a time, in from the right edge and out past the
left, and the same on a phone. So the track holds one copy now — the second
span and its `aria-hidden` are gone, and with them the reason the notice was
announced once instead of twice — and the keyframes run `translateX(100vw)` to
`translateX(-100%)`. The units differ because the two ends are measured in
different things: 100vw is the window, which is where the sentence starts, and
100% is the track, which is the sentence, and `-100%` is therefore exactly the
width of the string it has to clear. At rest the sentence sits wholly off the
right edge — left edge at 1440 on a 1440 window — and 30s later its right edge
is at 2.1, i.e. past the left edge, so an observer never sees two and never
sees half of one appear from nowhere.
30s rather than 40s, and this is the compromise worth naming: the trip is
100vw plus the sentence, and CSS cannot add a viewport unit to an element width
in a transform, so the duration is one number for both sizes. At 1440 the
sentence covers 2081px in 30s, at 390 it covers 1031px in the same 30s — the
phone walks it slower in pixels-per-second and the visitor on a phone is
waiting proportionally longer. Fitting both would need the width in a custom
property and a keyframe per breakpoint, which is machinery around a 12px line
of legal copy.
`padding-right: 72px` goes with the seam it was written for: that air was the
gap between two copies, and with one copy there is no between. The band keeps
its own 6px so the sentence is clipped at the band's edge and not at the
window's.
Under `prefers-reduced-motion` the animation was already off and the sentence
sat at the left edge of the band clipped in half. A static notice that is
half a sentence is not a notice, so the band is allowed to scroll there: the
track stops animating and `.lp-notice` gets `overflow-x: auto`, which is the
platform's own answer — the reader drags the line if they want its end, and
nothing moves on its own.
The band keeps its height, so the hardcoded offsets that pay for it — 148px of
scroll padding, 216px of hero top padding, 144px on mobile — are untouched.
Verified: npx tsc --noEmit clean, npm run build clean, the built CSS carries
`@keyframes lp-notice-roll{0%{transform:translate(100vw)}to{transform:translate(-100%)}}`
and `animation:lp-notice-roll 30s linear infinite`. In the running app through
a probe, sampled over one 30s cycle: one span in the band, no `aria-hidden`
span beside it, animation 30000ms linear, and the string's box tracked from
left 1440 / right 2081.3 at t=0, through 711.5/1352.9 at 10.5s, to -639.2/2.1
at 29.97s — entering exactly at the right edge and gone past the left. At
390x800 the same shape: 390/1031.3 at t=0 to -640.3/1 at 29.97s, so the phone
gets the whole crossing too. `overflow: 0` on the document at both widths,
i.e. a 100vw transform inside the clipped band adds no page-level scroll. The
band was viewed at both widths.
Co-authored-by: PenguinHarness <noreply@penguin.local>
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