This seems to be specific to custom vector base maps, rather than custom base maps in general?
Can you please be more specific about your question? A lot has changed since this webinar was recorded back in 2018.
@BernSzukalski How do I upload my custom style to Enterprise? I tried adding it through My Content, but it did not recognize the file.
Thanks! 🙂
Hopefully this Pro help document will get you pointed in the right direction. Note the caveats with different versions of Enterprise.
https://pro.arcgis.com/en/pro-app/latest/help/sharing/overview/share-a-web-style.htm
This Online help documents explains how those are used:
Wonderful, thank you very much @BernSzukalski!