Testing the app on an iPad, I noticed the subtitles are not rendered correctly and some styles are actually impossible to read because the text turns fully transparent.
You can recreate this by going into the accessibility settings (iOS), SDH subtitles and then changing the style. Based on what you select there, and especially if you set custom styles, the text can render something like this:
Hope it gets fixed and the style gets used properly following all the rules, thanks.
