Tweaks to the Home page examples

[badcat]

I like this. However I noticed a couple of things that might benefit from some minor adjustments.

Buttons:
Per the W3C validation...

The <button> element must not appear as a descendant of the <a> element.

Suggest removing these examples:

<a href="./"><button>a link button</button></a>
<a href="./"><button disabled>a disabled link button</button></a>

Break line:
Break line <hr> should probably be called Horizontal Rule.
Also, probably don't need to show <hr /> with trailing slash for default html5, but instead just <hr>

[badcat]

@louismerlin I created a quick PR if it makes sense to merge? Thanks for concrete.css

[louismerlin]

Very cool, thank you again for reporting 😄

I'll be using these sorts of tools more regularly, I had never ran across them.