03Line numbers with a called-out line

The line numbers are counted with counter-increment and printed in ::before, not typed as text, so they never tag along when you copy. The called-out line carries its own background, and pointing at it raises a note saying why it matters.

Best forTutorials that must explain exactly one line of a long file

counter-increment::beforeuser-select

<main class="stage">
  <div class="lnh is-demo" id="root">
    <div class="pane">
      <div class="pane__head">
        <span class="pane__lang">CSS</span>
      </div>
      <div class="pane__body">
        <pre id="codeText"><code class="lines"><span class="ln">.card {</span><span class="ln">  display: grid;</span><span class="ln is-called" id="calledLine" tabindex="0" aria-describedby="tip">  gap: 12px;</span><span class="ln">  padding: 16px;</span><span class="ln">}</span></code></pre>
      </div>
    </div>
    <div class="tooltip" id="tip" role="tooltip">Gap between cards</div>
    <span class="lnh__cursor" id="cursor" aria-hidden="true"></span>
  </div>
</main>

@use "../../../../site/static/demo-tokens" as *;

$duration: $dur-base;
$easing: $ease-spring;
$color: $subject-mint;

$syn-key: $stage-orange;
$syn-str: $stage-yellow;
$syn-num: $subject-sky;
$syn-dim: rgba($subject-cream, .72);
$syn-txt: $subject-cream;

@include stage($stage-orange);

.lnh {
  position: relative;
  box-sizing: border-box;
  padding-bottom: 48px;
}

.pane {
  box-sizing: border-box;
  width: 288px;
  border-radius: $r-card;
  overflow: hidden;
  box-shadow: $shadow-raised;
  background: $stage-ink;
  color: $subject-cream;
}

.pane__head {
  box-sizing: border-box;
  display: flex;
  align-items: center;
  gap: $sp-2;
  height: 28px;
  padding: 0 $sp-3;
  background: rgba(255, 247, 230, .06);
  border-bottom: 1px solid rgba(255, 247, 230, .12);
}
.pane__lang {
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: .02em;
  color: $syn-dim;
  text-transform: uppercase;
}

.pane__body {
  position: relative;
  box-sizing: border-box;
  padding: $sp-3;
  font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
  font-size: 11px;
  line-height: 18px;
}
.pane__body pre, .pane__body code { margin: 0; font: inherit; }
.lines { counter-reset: ln; display: block; }

.ln {
  position: relative;
  display: block;
  box-sizing: border-box;
  padding-left: 24px;
  color: $syn-txt;
  white-space: pre;
  border-radius: $r-xs;
}
.ln::before {
  counter-increment: ln;
  content: counter(ln);
  position: absolute;
  left: 0;
  top: 0;
  width: 16px;
  text-align: right;
  color: $syn-dim;
  user-select: none;
}
.ln.is-called {
  cursor: pointer;
  background: rgba($color, .10);
}
.ln.is-called:focus-visible { outline: 2px solid $color; outline-offset: 1px; }
.ln.is-called::after {
  content: "";
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 3px;
  border-radius: $r-xs;
  background: $color;
  transform-origin: top center; // 규칙8: 하이라이트 막대 위에서
  transform: scaleY(0);
}
.lnh.is-open .ln.is-called {
  background: rgba($color, .22);
  transition: background $duration $easing;
}
.lnh.is-open .ln.is-called::after {
  transform: scaleY(1);
  transition: transform $duration $easing;
}

.tooltip {
  // .pane 은 헤더 28px + 본문(패딩 $sp-3×2 + 5줄×18px) = 142px 로 고정 계산 가능 —
  // top:100% 는 .lnh 의 padding-bottom(예약분) 까지 포함해 계산되어 버리므로(Trap #7),
  // 반드시 .pane 실측 높이를 px 로 고정해 그 아래에 배치한다
  position: absolute;
  left: $sp-3;
  right: $sp-3;
  top: 142px;
  margin-top: $sp-2;
  box-sizing: border-box;
  padding: $sp-2 $sp-3;
  border-radius: $r-sm;
  background: rgba(255, 247, 230, .96);
  color: $stage-ink;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-size: 11px;
  font-weight: 700;
  box-shadow: $shadow-raised;
  opacity: 0;
  transform-origin: top center; // 규칙8: 패널 아래변에서 펼침
  transform: translateY(6px) scale(.96);
  pointer-events: none;
}
.lnh.is-open .tooltip {
  opacity: 1;
  transform: translateY(0) scale(1);
  transition: opacity $duration $easing, transform $duration $easing;
}

.lnh__cursor {
  position: absolute;
  left: 0;
  top: 0;
  z-index: 3;
  width: 12px;
  height: 12px;
  border: 2px solid $subject-cream;
  border-radius: 50%;
  background: $stage-ink;
  box-shadow: $shadow-press;
  pointer-events: none;
  opacity: 0;
  transform: translate(16px, 20px);
}
.lnh.is-demo .lnh__cursor { opacity: 1; }

// ── 자동 루프 (2s) ────────────────────────────────────
// 등장(≈9~19%, 0.2s)은 짧은 구간에 몰아 급격하게, 퇴장(≈78~94%)은 넓은 구간에 걸쳐 서서히
// — poster 가 「닫히는 순간」이 아니라 「짚어서 뜨는 순간」이 되도록 한다
.lnh.is-demo .tooltip {
  animation-name: lnh-tooltip;
  animation-duration: $dur-loop;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
.lnh.is-demo .ln.is-called {
  animation-name: lnh-bg;
  animation-duration: $dur-loop;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
.lnh.is-demo .ln.is-called::after {
  animation-name: lnh-bar;
  animation-duration: $dur-loop;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}
.lnh.is-demo .lnh__cursor {
  animation-name: lnh-cursor;
  animation-duration: $dur-loop;
  animation-timing-function: $easing;
  animation-iteration-count: infinite;
}

@keyframes lnh-tooltip {
  0%, 9%   { opacity: 0; transform: translateY(6px) scale(.96); }
  19%      { opacity: 1; transform: translateY(0) scale(1); }
  78%      { opacity: 1; transform: translateY(0) scale(1); }
  94%      { opacity: 0; transform: translateY(6px) scale(.96); }
  100%     { opacity: 0; transform: translateY(6px) scale(.96); }
}
@keyframes lnh-bg {
  0%, 18%  { background: rgba($color, .10); }
  20%      { background: rgba($color, .24); }
  74%      { background: rgba($color, .24); }
  92%      { background: rgba($color, .10); }
  100%     { background: rgba($color, .10); }
}
@keyframes lnh-bar {
  0%, 20%  { transform: scaleY(0); }
  34%      { transform: scaleY(1); }
  78%      { transform: scaleY(1); }
  94%      { transform: scaleY(0); }
  100%     { transform: scaleY(0); }
}
@keyframes lnh-cursor {
  // 3번 줄 글자("  gap: 12px;")는 절대좌표 x 36~115 에 찍힌다 — 커서는 그 오른쪽 빈칸(x≥130)에서만 훑는다
  0%, 2%    { transform: translate(16px, 20px); }
  18%       { transform: translate(150px, 84px); }
  34%       { transform: translate(180px, 84px); }
  52%       { transform: translate(140px, 84px); }
  72%       { transform: translate(170px, 84px); }
  86%, 100% { transform: translate(16px, 20px); }
}

@media (max-width: 340px) {
  // 좁은 폭에서 .pane 높이 = 헤더 28px + 본문(패딩 $sp-2×2 + 5줄×16px) = 124px
  .lnh { padding-bottom: 32px; }
  .pane { width: 100%; }
  .pane__body { font-size: 10px; line-height: 16px; padding: $sp-2; }
  .ln { padding-left: 20px; }
  .tooltip {
    top: 124px;
    margin-top: $sp-1;
    left: $sp-2;
    right: $sp-2;
    padding: $sp-1 $sp-2;
  }
}

@media (prefers-reduced-motion: reduce) {
  .lnh.is-demo .tooltip,
  .lnh.is-demo .ln.is-called,
  .lnh.is-demo .ln.is-called::after,
  .lnh.is-demo .lnh__cursor { animation: none !important; }
  .lnh.is-demo .lnh__cursor { opacity: 0; }
  .lnh.is-demo .tooltip { opacity: 0; }
}

html, body {
  margin: 0;
  overflow: hidden;
}

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ff4d1f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.lnh {
  position: relative;
  box-sizing: border-box;
  padding-bottom: 48px;
}

.pane {
  box-sizing: border-box;
  width: 288px;
  border-radius: 16px;
  overflow: hidden;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  background: #17141a;
  color: #fff7e6;
}

.pane__head {
  box-sizing: border-box;
  display: flex;
  align-items: center;
  gap: 8px;
  height: 28px;
  padding: 0 12px;
  background: rgba(255, 247, 230, 0.06);
  border-bottom: 1px solid rgba(255, 247, 230, 0.12);
}

.pane__lang {
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-size: 11px;
  font-weight: 700;
  letter-spacing: 0.02em;
  color: rgba(255, 247, 230, 0.72);
  text-transform: uppercase;
}

.pane__body {
  position: relative;
  box-sizing: border-box;
  padding: 12px;
  font-family: ui-monospace, "SFMono-Regular", Menlo, Consolas, monospace;
  font-size: 11px;
  line-height: 18px;
}

.pane__body pre, .pane__body code {
  margin: 0;
  font: inherit;
}

.lines {
  counter-reset: ln;
  display: block;
}

.ln {
  position: relative;
  display: block;
  box-sizing: border-box;
  padding-left: 24px;
  color: #fff7e6;
  white-space: pre;
  border-radius: 4px;
}

.ln::before {
  counter-increment: ln;
  content: counter(ln);
  position: absolute;
  left: 0;
  top: 0;
  width: 16px;
  text-align: right;
  color: rgba(255, 247, 230, 0.72);
  user-select: none;
}

.ln.is-called {
  cursor: pointer;
  background: rgba(76, 212, 166, 0.1);
}

.ln.is-called:focus-visible {
  outline: 2px solid #4cd4a6;
  outline-offset: 1px;
}

.ln.is-called::after {
  content: "";
  position: absolute;
  left: 0;
  top: 0;
  bottom: 0;
  width: 3px;
  border-radius: 4px;
  background: #4cd4a6;
  transform-origin: top center;
  transform: scaleY(0);
}

.lnh.is-open .ln.is-called {
  background: rgba(76, 212, 166, 0.22);
  transition: background 300ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.lnh.is-open .ln.is-called::after {
  transform: scaleY(1);
  transition: transform 300ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.tooltip {
  position: absolute;
  left: 12px;
  right: 12px;
  top: 142px;
  margin-top: 8px;
  box-sizing: border-box;
  padding: 8px 12px;
  border-radius: 8px;
  background: rgba(255, 247, 230, 0.96);
  color: #17141a;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  font-size: 11px;
  font-weight: 700;
  box-shadow: 0 14px 24px rgba(23, 20, 26, 0.32);
  opacity: 0;
  transform-origin: top center;
  transform: translateY(6px) scale(0.96);
  pointer-events: none;
}

.lnh.is-open .tooltip {
  opacity: 1;
  transform: translateY(0) scale(1);
  transition: opacity 300ms cubic-bezier(0.2, 0.8, 0.2, 1), transform 300ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.lnh__cursor {
  position: absolute;
  left: 0;
  top: 0;
  z-index: 3;
  width: 12px;
  height: 12px;
  border: 2px solid #fff7e6;
  border-radius: 50%;
  background: #17141a;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  pointer-events: none;
  opacity: 0;
  transform: translate(16px, 20px);
}

.lnh.is-demo .lnh__cursor {
  opacity: 1;
}

.lnh.is-demo .tooltip {
  animation-name: lnh-tooltip;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}

.lnh.is-demo .ln.is-called {
  animation-name: lnh-bg;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}

.lnh.is-demo .ln.is-called::after {
  animation-name: lnh-bar;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}

.lnh.is-demo .lnh__cursor {
  animation-name: lnh-cursor;
  animation-duration: 2s;
  animation-timing-function: cubic-bezier(0.2, 0.8, 0.2, 1);
  animation-iteration-count: infinite;
}

@keyframes lnh-tooltip {
  0%, 9% {
    opacity: 0;
    transform: translateY(6px) scale(0.96);
  }
  19% {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
  78% {
    opacity: 1;
    transform: translateY(0) scale(1);
  }
  94% {
    opacity: 0;
    transform: translateY(6px) scale(0.96);
  }
  100% {
    opacity: 0;
    transform: translateY(6px) scale(0.96);
  }
}
@keyframes lnh-bg {
  0%, 18% {
    background: rgba(76, 212, 166, 0.1);
  }
  20% {
    background: rgba(76, 212, 166, 0.24);
  }
  74% {
    background: rgba(76, 212, 166, 0.24);
  }
  92% {
    background: rgba(76, 212, 166, 0.1);
  }
  100% {
    background: rgba(76, 212, 166, 0.1);
  }
}
@keyframes lnh-bar {
  0%, 20% {
    transform: scaleY(0);
  }
  34% {
    transform: scaleY(1);
  }
  78% {
    transform: scaleY(1);
  }
  94% {
    transform: scaleY(0);
  }
  100% {
    transform: scaleY(0);
  }
}
@keyframes lnh-cursor {
  0%, 2% {
    transform: translate(16px, 20px);
  }
  18% {
    transform: translate(150px, 84px);
  }
  34% {
    transform: translate(180px, 84px);
  }
  52% {
    transform: translate(140px, 84px);
  }
  72% {
    transform: translate(170px, 84px);
  }
  86%, 100% {
    transform: translate(16px, 20px);
  }
}
@media (max-width: 340px) {
  .lnh {
    padding-bottom: 32px;
  }
  .pane {
    width: 100%;
  }
  .pane__body {
    font-size: 10px;
    line-height: 16px;
    padding: 8px;
  }
  .ln {
    padding-left: 20px;
  }
  .tooltip {
    top: 124px;
    margin-top: 4px;
    left: 8px;
    right: 8px;
    padding: 4px 8px;
  }
}
@media (prefers-reduced-motion: reduce) {
  .lnh.is-demo .tooltip,
  .lnh.is-demo .ln.is-called,
  .lnh.is-demo .ln.is-called::after,
  .lnh.is-demo .lnh__cursor {
    animation: none !important;
  }
  .lnh.is-demo .lnh__cursor {
    opacity: 0;
  }
  .lnh.is-demo .tooltip {
    opacity: 0;
  }
}

var root = document.getElementById('root');
var line = document.getElementById('calledLine');

function open() {
  root.classList.remove('is-demo');
  root.classList.add('is-open');
}
function close() {
  root.classList.remove('is-open');
}
line.addEventListener('mouseenter', open);
line.addEventListener('mouseleave', close);
line.addEventListener('focus', open);
line.addEventListener('blur', close);

import { useState } from "react";
import type { CSSProperties } from "react";
import styles from "./LineNumberHighlight.module.scss";

export type LineNumberHighlightProps = {
  langLabel?: string;
  tooltipText?: string;
  /** Auto-play loop (for gallery). Turns off on real interaction */
  demo?: boolean;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };

const LINES = [".card {", "  display: grid;", "  gap: 12px;", "  padding: 16px;", "}"];
const CALLED_INDEX = 2;

export default function LineNumberHighlight({
  langLabel = "CSS",
  tooltipText = "Gap between cards",
  demo = true,
  duration = 300,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#4cd4a6",
}: LineNumberHighlightProps) {
  const [live, setLive] = useState(demo);
  const [open, setOpen] = useState(false);
  const [tipId] = useState(() => "lnh-tip-" + Math.random().toString(36).slice(2));

  function show() {
    setLive(false);
    setOpen(true);
  }
  function hide() {
    setOpen(false);
  }

  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  return (
    <div className={[styles.lnh, live ? styles.isDemo : "", open ? styles.isOpen : ""].join(" ")} style={vars}>
      <div className={styles.pane}>
        <div className={styles.paneHead}>
          <span className={styles.paneLang}>{langLabel}</span>
        </div>
        <div className={styles.paneBody}>
          <pre>
            <code className={styles.lines}>
              {LINES.map((text, i) =>
                i === CALLED_INDEX ? (
                  <span
                    key={i}
                    className={[styles.ln, styles.isCalled].join(" ")}
                    tabIndex={0}
                    aria-describedby={tipId}
                    onMouseEnter={show}
                    onMouseLeave={hide}
                    onFocus={show}
                    onBlur={hide}
                  >
                    {text}
                  </span>
                ) : (
                  <span key={i} className={styles.ln}>
                    {text}
                  </span>
                )
              )}
            </code>
          </pre>
        </div>
      </div>
      <div className={styles.tooltip} id={tipId} role="tooltip">
        {tooltipText}
      </div>
      <span className={styles.lnhCursor} aria-hidden="true" />
    </div>
  );
}

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03 Line numbers with a called-out line — Measured area 14.751% · moving frames 22/23Original by GODRICH · SCSS and React ship in the zip · 9 Code Block UI Patterns — No Highlighter Library

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9 Code Block UI Patterns — No Highlighter Library - preview of all 9 demos

9 Code Block UI Patterns — No Highlighter LibraryA code block UI is the small frame built around a snippet — header, copy button, tabs — that tells a reader what they ar See all demos in this post

03Line numbers with a called-out line

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