The server knows the page but not where the reader has scrolled to, so a
reload part-way down painted the header from the page's own state and
corrected it once the backdrop had been measured. No script wins that race,
because the browser paints before parsing finishes. createContrastBootScript
remembers the state on pagehide and puts it back as CSS in the head, which
applies to elements as they are parsed; the runtime drops it in the same
frame as its first reading.