place the ".min.js" extension with ".js".
    -->
    <script defer src="packages/mdc_web/material-components-web.min.js"></script>
    <script defer src="main.dart.js"></script>
  </head>

  <body>
    <h2>mdc_web Example</h2>

    <button class="mdc-button mdc-button--raised"
      data-mdc-auto-init="MDCRipple">Auto Init!</button>
    <button class="mdc-button primary">Primary Button</button>
    <button class="mdc-button secondary">Secondary Button</button>
    <button class="mdc-button tertiary mdc-but