SpeedTest Checker Tool

Please note that you need to replace the runSpeedTest function with actual speed test logic using an appropriate library or API. A popular choice for speed testing is the Speedtest.net API, but you'll need to sign up for an account and get an API key. Also, for a fully responsive and SEO-friendly design, make sure your HTML structure is semantic, and consider adding meta tags for SEO. Responsive design is already taken care of in the provided example.