It's in Vue, and surface ui. There's also a pending @scope keyword coming to CSS in the near future. I'd expect most component frameworks to have some equivale

It's in Vue, and surface ui. There's also a pending @scope keyword coming to CSS in the near future. I'd expect most component frameworks to have some equivalent version of this. In svelte, it's the default; all style tags written inside a component are scoped to said component. You can largely achieve scoping manually if you have to, via nesting, which recently landed in CSS.