Current Declarative Shadow DOM browser support:
Chrome 90, Edge 90, Samsung Internet 15
`<template shadowroot="open">`
Chrome 111, Safari Technology Preview 162
`<template shadowrootmode="open">`
It’s tempting to use both `<template shadowroot="open" shadowrootmode="open">` for the broadest browser support, hmm.
https://caniuse.com/mdn-html_elements_template_shadowrootmode