Web Components, Shadow Dom, Web Standards, CSS, HTML.
display: block; color: red; } </style> Hello World </template> </hello-world> <hello-world> <template shadowrootmode="open"> <style> :host { display: block; color: red; } </style> Hello World </template> </hello-world> <hello-world> <template shadowrootmode="open"> <style> :host { display: block;