The chrome is now authored against Firefox design-token names with the shipped
value as a fallback `var(--fx-token, <literal>)` so colors, borders and radii
follow Firefox instead of having to be re-synced by hand.
In MOZCENTRAL viewer.css imports chrome://global/skin/design-system/tokens-brand.css,
gated on the new pdfjs.enableNova pref (default false, read straight from CSS via -moz-pref()).
With the pref off the sheet isn't applied, every fallback resolves, and the
viewer renders as before, as it also does in the GENERIC and components builds,
which never see the chrome sheet.
Consuming a token means never declaring its name in an unlayered rule, which
would shadow Firefox's for the whole subtree; --focus-outline, --border-color and
--text-color/--button-border-color are therefore renamed to
--editor-selection-outline, --signature-border-color and --views-*. In forced
colors each state reads a matching background/foreground/border triple so it
can't collapse to a single system color.
The dialog button styling also moves out of `.dialog .mainContainer button` into
a shared .primaryButton/.secondaryButton primitive (buttons.css, imported from
pdf_viewer.css so the components build gets it too). The password,
document-properties, print and undo-bar buttons use it in place of .dialogButton,
and the custom radio appearance gives way to native controls tinted with
accent-color.
The goal is to be able to catch the errors before making a release.
And fix some css issues (especially the missing css code for the newly added menu.css)
