02Keyboard highlight rail

<main class="stage">
  <div class="kb is-demo">
    <span class="kb__label" id="kb-label">Sort by</span>
    <div class="kb__panel">
      <div class="kb__rail" aria-hidden="true"></div>
      <ul class="kb__list" id="kb-list" role="listbox" aria-labelledby="kb-label" tabindex="0" aria-activedescendant="kb-o1">
        <li class="kb__opt" id="kb-o1" role="option" aria-selected="true">Newest</li>
        <li class="kb__opt" id="kb-o2" role="option" aria-selected="false">Most popular</li>
        <li class="kb__opt" id="kb-o3" role="option" aria-selected="false">Price: low to high</li>
        <li class="kb__opt" id="kb-o4" role="option" aria-selected="false">Price: high to low</li>
      </ul>
    </div>
    <span class="kb__hint">↑ ↓ Home End</span>
  </div>
</main>

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

$duration: $dur-quick;
$easing: $ease-spring;
$color: $subject-blue;

@include stage($stage-yellow);

.kb {
  box-sizing: border-box;
  width: min(216px, 84vw);
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: $stage-ink;
}
.kb__label {
  display: block;
  font-size: 10px; line-height: 12px; font-weight: 800;
  letter-spacing: .04em;
  color: rgba(23, 20, 26, .72);
  margin: 0 0 $sp-1;
}
.kb__panel {
  position: relative;
  box-sizing: border-box;
  padding: $sp-1;
  background: #fff;
  border-radius: $r-card;
  box-shadow: $shadow-press;
}
.kb__rail {
  position: absolute;
  top: $sp-1; left: $sp-1; right: $sp-1;
  height: 28px;
  border-radius: $r-sm;
  background: rgba(47, 109, 246, .14);
  box-shadow: inset 0 0 0 1px rgba(47, 109, 246, .35);
  transform: translateY(0);
  transition: transform $duration $easing;
}
.kb__list { margin: 0; padding: 0; list-style: none; position: relative; }
.kb__list:focus-visible { outline: 2px solid $color; outline-offset: 4px; border-radius: $r-sm; }
.kb__opt {
  box-sizing: border-box;
  height: 28px;
  display: flex; align-items: center;
  padding: 0 $sp-2;
  font-size: 12px; font-weight: 600;
  color: rgba(23, 20, 26, .7);
  cursor: pointer;
}
.kb__opt.is-at { color: $color; }
.kb__opt.is-sel { font-weight: 800; }
.kb__hint {
  display: block;
  margin: $sp-2 0 0;
  font-size: 10px; font-weight: 700;
  letter-spacing: .08em;
  color: rgba(23, 20, 26, .72);
}

// ── 자동 루프: 막대가 1→4 로 내려갔다 다시 1 로 올라온다. 되돌아오므로 이음새가 없다 ──
.kb.is-demo .kb__rail { animation: kb-rail $dur-loop $ease-spring infinite; }
@keyframes kb-rail {
  0%   { transform: translateY(0); }
  17%  { transform: translateY(28px); }
  34%  { transform: translateY(56px); }
  50%  { transform: translateY(84px); }
  67%  { transform: translateY(56px); }
  84%  { transform: translateY(28px); }
  100% { transform: translateY(0); }
}

@media (prefers-reduced-motion: reduce) {
  .kb.is-demo .kb__rail { animation: none !important; }
  .kb__rail { transition: none; }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #ffd23f;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.kb {
  box-sizing: border-box;
  width: min(216px, 84vw);
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  color: #17141a;
}

.kb__label {
  display: block;
  font-size: 10px;
  line-height: 12px;
  font-weight: 800;
  letter-spacing: 0.04em;
  color: rgba(23, 20, 26, 0.72);
  margin: 0 0 4px;
}

.kb__panel {
  position: relative;
  box-sizing: border-box;
  padding: 4px;
  background: #fff;
  border-radius: 16px;
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
}

.kb__rail {
  position: absolute;
  top: 4px;
  left: 4px;
  right: 4px;
  height: 28px;
  border-radius: 8px;
  background: rgba(47, 109, 246, 0.14);
  box-shadow: inset 0 0 0 1px rgba(47, 109, 246, 0.35);
  transform: translateY(0);
  transition: transform 220ms cubic-bezier(0.2, 0.8, 0.2, 1);
}

.kb__list {
  margin: 0;
  padding: 0;
  list-style: none;
  position: relative;
}

.kb__list:focus-visible {
  outline: 2px solid #2f6df6;
  outline-offset: 4px;
  border-radius: 8px;
}

.kb__opt {
  box-sizing: border-box;
  height: 28px;
  display: flex;
  align-items: center;
  padding: 0 8px;
  font-size: 12px;
  font-weight: 600;
  color: rgba(23, 20, 26, 0.7);
  cursor: pointer;
}

.kb__opt.is-at {
  color: #2f6df6;
}

.kb__opt.is-sel {
  font-weight: 800;
}

.kb__hint {
  display: block;
  margin: 8px 0 0;
  font-size: 10px;
  font-weight: 700;
  letter-spacing: 0.08em;
  color: rgba(23, 20, 26, 0.72);
}

.kb.is-demo .kb__rail {
  animation: kb-rail 2s cubic-bezier(0.2, 0.8, 0.2, 1) infinite;
}

@keyframes kb-rail {
  0% {
    transform: translateY(0);
  }
  17% {
    transform: translateY(28px);
  }
  34% {
    transform: translateY(56px);
  }
  50% {
    transform: translateY(84px);
  }
  67% {
    transform: translateY(56px);
  }
  84% {
    transform: translateY(28px);
  }
  100% {
    transform: translateY(0);
  }
}
@media (prefers-reduced-motion: reduce) {
  .kb.is-demo .kb__rail {
    animation: none !important;
  }
  .kb__rail {
    transition: none;
  }
}

// 실제 동작: 화살표·Home·End 로 하이라이트 막대가 옮겨 다니고, Enter 로 그 줄이 선택된다.
var root = document.querySelector('.kb');
var list = document.getElementById('kb-list');
var rail = document.querySelector('.kb__rail');
var opts = [].slice.call(list.querySelectorAll('.kb__opt'));
var ROW = 28;
var at = 0;
function move(i) {
  root.classList.remove('is-demo');
  at = Math.max(0, Math.min(i, opts.length - 1));
  rail.style.transform = 'translateY(' + (at * ROW) + 'px)';
  list.setAttribute('aria-activedescendant', opts[at].id);
  opts.forEach(function (o, k) { o.classList.toggle('is-at', k === at); });
}
function choose() {
  opts.forEach(function (o, k) {
    o.setAttribute('aria-selected', String(k === at));
    o.classList.toggle('is-sel', k === at);
  });
}
list.addEventListener('keydown', function (e) {
  if (e.key === 'ArrowDown') { move(at + 1); e.preventDefault(); }
  else if (e.key === 'ArrowUp') { move(at - 1); e.preventDefault(); }
  else if (e.key === 'Home') { move(0); e.preventDefault(); }
  else if (e.key === 'End') { move(opts.length - 1); e.preventDefault(); }
  else if (e.key === 'Enter' || e.key === ' ') { choose(); e.preventDefault(); }
});
opts.forEach(function (o, i) {
  o.addEventListener('click', function () { move(i); choose(); });
});

import { useRef, useState } from "react";
import type { CSSProperties } from "react";
import styles from "./HighlightRail.module.scss";

export type HighlightRailProps = {
  label?: string;
  options?: string[];
  hint?: string;
  duration?: number;
  easing?: string;
  color?: string;
};

type Vars = CSSProperties & { "--duration"?: string; "--easing"?: string; "--color"?: string };
type KeyEvt = { key: string; preventDefault: () => void };
type ChangeEvt = { target: { value: string } };
type ClickEvt = { stopPropagation: () => void };

const ROW = 28;

export default function HighlightRail({
  label = "Sort by",
  options = ["Newest", "Most popular", "Price: low to high", "Price: high to low"],
  hint = "↑ ↓ Home End",
  duration = 220,
  easing = "cubic-bezier(.2,.8,.2,1)",
  color = "#2f6df6",
}: HighlightRailProps) {
  const [at, setAt] = useState(0);
  const [picked, setPicked] = useState(0);
  const listRef = useRef<HTMLUListElement>(null);
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };

  function move(i: number) {
    setAt(Math.max(0, Math.min(i, options.length - 1)));
  }

  return (
    <div className={styles.kb} style={vars}>
      <span className={styles.label} id="kb-label">{label}</span>
      <div className={styles.panel}>
        <div
          className={styles.rail}
          aria-hidden="true"
          style={{ transform: `translateY(${at * ROW}px)` }}
        />
        <ul
          ref={listRef}
          id="kb-list"
          className={styles.list}
          role="listbox"
          aria-labelledby="kb-label"
          aria-activedescendant={`kb-o${at}`}
          tabIndex={0}
          onKeyDown={(e: KeyEvt) => {
            if (e.key === "ArrowDown") { move(at + 1); e.preventDefault(); }
            else if (e.key === "ArrowUp") { move(at - 1); e.preventDefault(); }
            else if (e.key === "Home") { move(0); e.preventDefault(); }
            else if (e.key === "End") { move(options.length - 1); e.preventDefault(); }
            else if (e.key === "Enter" || e.key === " ") { setPicked(at); e.preventDefault(); }
          }}
        >
          {options.map((o, i) => (
            <li
              key={o}
              id={`kb-o${i}`}
              className={`${styles.opt} ${i === at ? styles.isAt : ""} ${i === picked ? styles.isSel : ""}`}
              role="option"
              aria-selected={i === picked}
              onClick={() => {
                move(i);
                setPicked(i);
                listRef.current?.focus({ preventScroll: true });
              }}
            >
              {o}
            </li>
          ))}
        </ul>
      </div>
      <span className={styles.hint}>{hint}</span>
    </div>
  );
}