prism-line-highlight.css

pre[data-line] {
	position: relative;
	padding: 1em 0 1em 3em;
}

.line-highlight {
	position: absolute;
	left: 0;
	right: 0;
	padding: inherit 0;
	margin-top: 1em; /* Same as .prism’s padding-top */

	background: hsla(24, 20%, 50%,.08);
	background: linear-gradient(to right, hsla(24, 20%, 50%,.1) 70%, hsla(24, 20%, 50%,0));

	pointer-events: none;

	line-height: inherit;
	white-space: pre;
}

	.line-highlight:before,
	.line-highlight[data-end]:after {
		content: attr(data-start);
		position: absolute;
		top: .4em;
		left: .6em;
		min-width: 1em;
		padding: 0 .5em;
		background-color: hsla(24, 20%, 50%,.4);
		color: hsl(24, 20%, 95%);
		font: bold 65%/1.5 sans-serif;
		text-align: center;
		vertical-align: .3em;
		border-radius: 999px;
		text-shadow: none;
		box-shadow: 0 1px white;
	}

	.line-highlight[data-end]:after {
		content: attr(data-end);
		top: auto;
		bottom: .4em;
	}

.line-numbers .line-highlight:before,
.line-numbers .line-highlight:after {
	content: none;
}

pre[id].linkable-line-numbers span.line-numbers-rows {
	pointer-events: all;
}
pre[id].linkable-line-numbers span.line-numbers-rows > span:before {
	cursor: pointer;
}
pre[id].linkable-line-numbers span.line-numbers-rows > span:hover:before {
	background-color: rgba(128, 128, 128, .2);
}