Newsletter Subscription Popup Integration

I’d like a clean, responsive modal popup that invites visitors to join my newsletter. The focus is on a smooth user experience and an easy-to-edit setup so I can adjust copy, styling, and display rules without touching core code each time.

Here’s what I need you to handle:
• Design a branded popup (desktop and mobile) that fades in/out smoothly and does not slow page load.
• Build the HTML/CSS/JavaScript for the modal and add any lightweight libraries you feel are appropriate (vanilla JS or something like jQuery if truly necessary).
• Integrate the form with my email list provider (Mailchimp, Klaviyo, or a simple form-to-email script—let’s decide together). The visitor should see a short confirmation message once their address is accepted.
• Give me straightforward controls for when and where the popup appears (delay timer, exit-intent, specific pages, etc.) so I can fine-tune behavior from a single config file or CMS settings.
• Final deliverables: source files, clear install notes for my developer workflow, and a quick demo recording or screenshots showing it working on a live page.

The code must be standards-compliant, accessible, and tested on the latest versions of Chrome, Safari, Firefox, and Edge, plus iOS and Android browsers.