Here is an example of using the Notifications Panel in a plain html page:
Update code below:
<html>
<head>
<link href="https://developer.temenos.com/uux/base.css" rel="stylesheet" />
<script src="https://developer.temenos.com/uux/unified-ux-web.min.js"></script>
</head>
<body>
<uwc-button label="Show default notification" contained
@click=${
() => document.getElementById('notifications-panel').enqueueNotification("I'm a default notification.")
}></uwc-button>
<uwc-notifications-panel id="notifications-panel" vertical="top"></uwc-notifications-panel>
</body>
</html>