Toast Notifications with the Native Popover API (No JS Library)

Stackable toast notifications built on the native HTML Popover API - the whole toast stack lives inside a single element with the popover attribute, so it always renders in the browser's top layer above everything else on the page, with zero z-index tuning. Each toast fades and slides in, auto-dismisses after 4 seconds, and removes itself from the DOM afterwards. Copy the HTML, CSS and JS below and drop it into any project.