Is it possible to change subtitle appearance on AirPlay from Safari?

It seems possible to achieve this with the iOS Native SDK at least for WebVTT subtitles:

func onReady(_ event: ReadyEvent) {
        AVTextStyleRule(textMarkupAttributes: [
             kCMTextMarkupAttribute_CharacterEdgeStyle as String: kCMTextMarkupCharacterEdgeStyle_DropShadow,
             kCMTextMarkupAttribute_BackgroundColorARGB as String: [1.0, 0.0, 0.0, 1.0],
             kCMTextMarkupAttribute_BaseFontSizePercentageRelativeToVideoHeight as String: 5.5,

Is it possible to achieve the same with the Web SDK in Safari ?