<head> 
 <script src="https://cdn.onesignal.com/sdks/OneSignalSDK.js" async='async'></script>
  <script>
    var OneSignal = window.OneSignal || [];
    OneSignal.push(["init", {
      appId: "YOUR_APP_ID",
      autoRegister: false, /* Set to true to automatically prompt visitors */
      httpPermissionRequest: {
        enable: true
      },
      notifyButton: {
          enable: true /* Set to false to hide */
      }
    }]);
  </script>
</head>