One fixed size cannot suit everyone — the default was too big, then
too small. The subtitle menu in the transport bar now carries an
Appearance section: Size (S/M/L/XL), Font (Sans/Serif/Mono) and Place
(Bottom/Raised/Top). Choices apply at once and are remembered across
videos and launches, like every other preference.
Size and face are written into a style element rather than the
stylesheet: ::cue takes no custom properties, so the values have to be
literal.
Placement is not a CSS property at all — WebVTT carries position on the
cue — so it is rewritten into the cues themselves and the track re-cut.
Every source is text now, including the sidecars beside older
downloads, so all three can be placed the same way.
The default lands at 85%, between WebKit's own size and the 58% that
replaced it.
Re-cutting a track exposed a bug in the guard that applies the
subtitle preference: it keyed on how many text tracks there were, and
re-cutting one leaves that unchanged, so the fresh track would have
stayed disabled and the subtitles would have vanished on any change of
Place. It keys on the tracks themselves.