Custom theme for custom visuals in theme.json

I want to format the Timeline 2.4.0 in my themes.json file and import that theme in my other reports too. The problem is I don't know the properties of this custom visual. I don't want to format this timeline control with the visual level formatting options since there will be a lot of repetition to reproduce the same effect in other reports. Can somebody help me with that?

Here is the link of that custom visual: https://appsource.microsoft.com/en-us/product/power-bi-visuals/wa104380786?tab=overview&exp=ubp8