Put focus in the demo and press Tab. In the broken state there is nothing to land on.
Example
example.com
Semantic HTML sticker pack — $4
Add to cart
Cart:
Markup
Edit the HTML. The example above is live in this page, so Tab and a
screen reader read it the same way they would on any other site.
<divclass="lab-card"><pclass="lab-price">Semantic HTML sticker pack — $4</p><divclass="lab-btn lab-btn--fake"data-action="cart">Add to cart</div><pclass="lab-out">Cart: <outputdata-cart>0</output></p></div>