LitElement with embed a scss (for IE).

some-component.ts

import { LitElement, html, unsafeCSS } from 'lit-element';
import style from './scss/style.scss';

@customElement('some-component')
export default class SomeComponent extends LitElement {
  static get styles() {
    return [
      // If you don't need to consider IE, you can use a link tag to include style in the render function.
      unsafeCSS(style),
    ]
  }
  render() {
     html`<div>hello, world</div>`
  }
}

style.scss

body {
  background-color: white;
}

webpack.config.js

    module: {
      rules: [
        {
          test: /\.s[ac]ss$/i,
          use: [
            'raw-loader',
            'sass-loader',
          ],
        },
      ],
    },