import {LitElement, css, html} from 'lit-element'; class MyElement extends LitElement { static styles = css` .spinner { width: 32px; height: 32px; margin: 10px auto; border: 4px #ddd solid; border-top: 4px blue solid; border-radius: 50%; animation: spinner-anime 1.0s infinite linear; } @keyframes spinner-anime { 100% { transform: rotate(360deg); } } `; render() { return html` <div> <slot name="another-icon"> <div class="spinner"></div> </slot> <slot name="another-icon"> <div class="spinner"></div> <slot> </div> `; } } customElements.define('spinner-slot', MyElement);