shadow-dom-element/demo/template.html

shadow-dom-element is a declarative custom element/web component to render local and remote template

<style> :host{ box-shadow: 0 0 .5rem purple inset;
    display: inline-block; }</style>

<slot name="slot1"><h5>FAIL heading 5</h5></slot>
<slot name="slot2">
    <button>FAIL action</button>
</slot>
<slot name="slot3"><p> slot 3 not overridden </p></slot>
default slot