Responsive QR Code with Html and Css

You can set the container in the middle of the screen whatever user changes it when you add these properties to it in CSS:

.container {
  display: absolute;
  top:50%;
  left: 50%;
  transform: translate(-50%, -50%);
}

the new feature is transform, it has many lovely properties you can discover, I personally love it. Hope it's useful

1)Read about h1 tag its the most important and every website should have atleast one https://www.semrush.com/blog/h1-tag/

2)responsiveness is handled ,that's great .

3)image doesn't seems to be center in your site, so you need to learn to center some ways are that you can read about - min height to be used in body read about translate property or marging auto properties

All the best