Using :not as @supports.

dabblet.css

/**
 * Using :not as @supports.
 */

article
{
	background-color: #7e7;
	font-family: Droid Sans, Helvetica, Arial, sans;
}

article ul
{
	border: black solid thin;
	margin: 1em 1.5em;
	list-style: none;
}

/* middle elements */
article ul:not(:first-child):not(:last-child)
{
	border-width: 0 thin;
	margin-top: 0;
	margin-bottom: 0;
}

/* first element */
article ul:first-child:not(:last-child)
{
	border-width: thin thin 0 thin;
	margin-bottom: 0;
}

/* last element */
article ul:not(:first-child):last-child
{
	border-width: 0 thin thin thin;
	margin-top: 0;
}

dabblet.html

<article>
	<ul>
		<li>A
		<li>B
	</ul>

	<ul>
		<li>A
		<li>B
	</ul>

	<ul>
		<li>A
		<li>B
	</ul>
</article>

<article>	
	<ul>
		<li>A
		<li>B
	</ul>

	<ul>
		<li>A
		<li>B
	</ul>
</article>

<article>
	<ul>
		<li>A
		<li>B
	</ul>
</article>

dabblet.js

// alert('Hello world!');

settings.json

{"view":"split","fontsize":"100","seethrough":"","prefixfree":"1","page":"css"}