Mike Hartington glows about how good and useful the Shadow DOM is:
… Read article “Shadow DOM in Ionic”
[Shadow DOM is] actually built on two simple ideas, isolation and location. Need to create a bit of DOM that is isolated from the global scope? Shadow DOM is here to help. Need to specify the exact location of a piece of DOM? Shadow DOMs scope API is what you need!
It can be helpful to think of components that use Shadow DOM as modules for HTML. Markup