Multi step form using web components (template, slots)

What specific areas of your project would you like help with?

I got errors in html validator. I had created add-on custom element, add-on elements children are custom elements as well. I had checked html tree structure all children are defined before main add-on element. Also I had checked JavaScript written for children templates elements. Here is a error list https://github.com/ShubhamOulkar/frontend/issues/23. I need help on this.