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The WebVTT specification, https://w3c.github.io/webvtt/, mentions that color (and any other formatting) of cue text can be set using the "::cue" CSS extension.I tried the simple vtt file:WEBVTT::cue(#first_cue) { color: blue }X-TIMESTAMP-MAP=LOCAL:00:00:00.000,MPEGTS:0first_cue00:00:00.000 --> 00:00:10.000Allo world!without any success.What is the simplest implementation that would allow coloring/formatting of cue text?