The ::content pseudo-element is being replaced in future implementations of Web Components / Shadow DOM with the ::slotted pseudo-element. Likewise, the element targeted by this pseudo-element has changed from <content to <slot> in the latest version of the Shadow DOM specification. You can see related discussion about that change here. Currently browsers still support <content> … Read more
As Joel H. points out in the comments, Chrome has since deprecated the /deep/ combinator, and it gives a syntax error in IE. HTML5 Web Components offer full encapsulation of CSS styles. This means that: styles defined within a component cannot leak out and effect the rest of the page styles defined at the page … Read more
They are different things for different purposes, so comparing performance doesn’t make sense. Virtual DOM Virtual DOM is about avoiding unnecessary changes to the DOM, which are expensive performance-wise, because changes to the DOM usually cause re-rendering of the page. Virtual DOM also allows to collect several changes to be applied at once, so not … Read more