This page has a neat effect, first apparent with this example, where a blur effect is used on most of the text in the code block, except for lines 11–13 which are shown in sharp focus. (You can mouse over the code block to eliminate the blur effect.)

.torchlight.has-focus-lines .line:not(.line-focus) {
        transition: filter 0.35s, opacity 0.35s;
        filter: blur(.095rem);
        opacity: .65;
}

Each line is dumped into a div and the line-focus class set on those which are supposed to be unblurred.

(For ordinary code blocks without any blur/focus effect, the has-focus-class line is simply not used.)