https://developer.mozilla.org/en-US/docs/Web/Web_Components/Using_shadow_DOM
<link rel="stylesheet" href="reset.css">
webpack を使って @import 'reset.css';
all: initial;
all: unset;
<x-foo> #shadow-root <div part="some-box"><span>...</span></div> <input part="some-input"> <div>...</div> /* not styleable </x-foo>
x-foo::part(some-box) { /* ... */ }
https://meowni.ca/posts/part-theme-explainer/
By katashin
Meguro.css #4 @ oRo https://megurocss.connpass.com/event/103713/