What is a Custom Element / Web Component?

Implementing a simplest possible Custom Element / Web Component.

[dextar]

Thanks a lot. Simplest intro to custom elements I've seen around. To the point, wow.

[rudythorns]

thats quick but precise thank you sir

[christophersanders]

great content a great developer and teacher

[Oswee]

You could cover styling options and patterns in context of complete applications based on LitElement. When to use external styles, when to use adoptedStylesheets and when to use ShadowDOM. As well to mention css custom properties. Also it's worth to mention that extends HTMLElement is pretty low level API and some should not it compare with something like React.