Well, speed is one reason. Because this is a newer API, you might first want to check that Shadow Parts are supported by the browsers you intend to target: browser support (both Chrome for Android and iOS Safari support the API). Important¶. 4. ! That being said, there is the on-going ::part and ::theme proposal that would allow components to safely expose some of their internals outside their shadow tree to be customized. About a year ago, Twitter announced it would start displaying embedded tweets with the shadow DOM rather than an