Fix HTML validity errors in html/static/main.html (<input> tag)
Fix HTML validity errors in html/static/main.html (<input> tag)

The HTML <input> tag is a singleton. That is to say, it can be used by
itself (just <input>), or used as a singleton XML tag (<input />), but
using an opening and a closing tag (<input></input>) is incorrect.

hastexo/hastexo-xblock,hastexo/hastexo-xblock,hastexo/hastexo-xblock,hastexo/hastexo-xblock