JSFiddle - React, Tailwind, and code Playground

HTML

<base href="https://polygit2.appspot.com/components/">
<link href="polymer/polymer.html" rel="import">
<link href="paper-spinner/paper-spinner.html" rel="import">
<link href="iron-overlay-behavior/iron-overlay-behavior.html" rel="import">

<x-test id="test" with-backdrop></x-test>
<button onclick="test.open()">
open
</button>

<style is="custom-style">
iron-overlay-backdrop {
  --iron-overlay-backdrop-background-color: #fff;
  --iron-overlay-backdrop-opacity: 0.9;
}
</style>

<dom-module id="x-test">
  <template>
    <paper-spinner active></paper-spinner>
  </template>
</dom-module>

JavaScript

Polymer({
	is: 'x-test',
  behaviors: [
  	Polymer.IronOverlayBehavior
  ]
})