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; }