our-app.js

import { LitElement, html } from 'lit-element'
import '@material/mwc-dialog'
import '@material/mwc-button'

class OurApp extends LitElement {
  render() {
    return html`
    <mwc-dialog title="Are you sure ?" open @closed=${this.onDialogClose}>
      <div>are you sure to perform this action ?</div>
      <mwc-button slot=secondaryAction dialogAction=no></mwc-button>
      <mwc-button slot=primaryAction dialogAction=yes raised></mwc-button>
    </mwc-dialog>
    `
  }
  
  onDialogClose (e) {
    if (e.detail.action === 'yes') {
      alert('BOOM')
    }
    else if (e.detail.action === 'no') {
      alert('nothing happens')
    }
  }
}