Update demo.js
    - [html] added span.* tags for windowState use
    - [css] added span.* default styling
    - [css] changed the min-width of small screen from 20em to 12.5em
    - [css] added the styling of .sm, .md, .lg, and .xl classes based on specific media queries
    - [js] used jQuery to test for a changed CSS property rather than the $(window).width() method
    NOTE: * - .sm | .md | .lg | .xl