02Glass navbar

<main class="stage">
  <nav class="gn-nav is-demo" aria-label="demo">
    <span class="gn-pill" aria-hidden="true"></span>
    <a class="gn-link" href="#">Home</a>
    <a class="gn-link" href="#">Docs</a>
    <a class="gn-link" href="#">Pricing</a>
  </nav>
</main>

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

// ── 변수 3개 ──────────────────────────────────────────
$duration: $dur-quick;
$easing: $ease-pop;
$color: $subject-blue;

@include stage($stage-yellow);

// 라벨 폭을 고정값으로 둔다 — translateX 만 쓰고 scaleX 는 안 쓰므로 BD19(flex 분배) 대상은 아니지만,
// 실제 폭이 흔들리면 필이 라벨 밖으로 걸리는 건 매한가지라 flex:0 0 auto + 고정 width 로 고정한다
$w: 76px;

.gn-nav {
  position: relative;
  box-sizing: border-box;
  width: min(272px, 86vw);
  display: flex;
  gap: $sp-2;
  padding: $sp-2;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .14);
  border: 1px solid rgba(255, 255, 255, .3);
  backdrop-filter: blur(14px) saturate(160%);
  -webkit-backdrop-filter: blur(14px) saturate(160%);
  box-shadow: $shadow-press;
}

.gn-link {
  position: relative;
  z-index: 1;
  flex: 0 0 auto;
  box-sizing: border-box;
  width: $w;
  text-align: center;
  padding: $sp-2 0;
  border-radius: $r-pill;
  font: 600 12px/1 -apple-system, "Segoe UI", sans-serif;
  color: $subject-ink;
  text-decoration: none;
}

.gn-pill {
  position: absolute;
  top: $sp-2; left: $sp-2; bottom: $sp-2;
  box-sizing: border-box;
  width: $w;
  border-radius: $r-pill;
  background: rgba(255, 255, 255, .6);
  backdrop-filter: blur(6px);
  box-shadow: $shadow-press;
  transform: translateX(0);
  transition: transform $duration $easing;
}

// 실사용: 진짜 호버로 필이 그 링크 아래로 이동 (:has 로 형제 상태를 읽는다)
.gn-nav:has(.gn-link:nth-child(3):hover) .gn-pill { transform: translateX(calc(#{$w} + #{$sp-2})); }
.gn-nav:has(.gn-link:nth-child(4):hover) .gn-pill { transform: translateX(calc((#{$w} + #{$sp-2}) * 2)); }

// 데모 루프: is-demo 는 세 자리를 keyframes 로 오간다 (헤드리스는 :has(:hover) 를 못 건다)
@keyframes gn-loop {
  0%, 15%  { transform: translateX(0); }
  33%, 48% { transform: translateX(calc(#{$w} + #{$sp-2})); }
  66%, 81% { transform: translateX(calc((#{$w} + #{$sp-2}) * 2)); }
  100%     { transform: translateX(0); }
}
.gn-nav.is-demo .gn-pill { animation: gn-loop $dur-loop $easing infinite; }

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

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);
}

.gn-nav {
  position: relative;
  box-sizing: border-box;
  width: min(272px, 86vw);
  display: flex;
  gap: 8px;
  padding: 8px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.14);
  border: 1px solid rgba(255, 255, 255, 0.3);
  backdrop-filter: blur(14px) saturate(160%);
  -webkit-backdrop-filter: blur(14px) saturate(160%);
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
}

.gn-link {
  position: relative;
  z-index: 1;
  flex: 0 0 auto;
  box-sizing: border-box;
  width: 76px;
  text-align: center;
  padding: 8px 0;
  border-radius: 999px;
  font: 600 12px/1 -apple-system, "Segoe UI", sans-serif;
  color: #17141a;
  text-decoration: none;
}

.gn-pill {
  position: absolute;
  top: 8px;
  left: 8px;
  bottom: 8px;
  box-sizing: border-box;
  width: 76px;
  border-radius: 999px;
  background: rgba(255, 255, 255, 0.6);
  backdrop-filter: blur(6px);
  box-shadow: 0 6px 12px rgba(23, 20, 26, 0.32);
  transform: translateX(0);
  transition: transform 220ms cubic-bezier(0.2, 1.4, 0.4, 1);
}

.gn-nav:has(.gn-link:nth-child(3):hover) .gn-pill {
  transform: translateX(calc(76px + 8px));
}

.gn-nav:has(.gn-link:nth-child(4):hover) .gn-pill {
  transform: translateX(calc((76px + 8px) * 2));
}

@keyframes gn-loop {
  0%, 15% {
    transform: translateX(0);
  }
  33%, 48% {
    transform: translateX(calc(76px + 8px));
  }
  66%, 81% {
    transform: translateX(calc((76px + 8px) * 2));
  }
  100% {
    transform: translateX(0);
  }
}
.gn-nav.is-demo .gn-pill {
  animation: gn-loop 2s cubic-bezier(0.2, 1.4, 0.4, 1) infinite;
}

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

import { CSSProperties } from "react";
import styles from "./GlassNavbar.module.scss";

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

export interface GlassNavbarProps {
  duration?: string;
  easing?: string;
}

const LINKS = ["Home", "Docs", "Pricing"];

export default function GlassNavbar({
  duration = "220ms",
  easing = "cubic-bezier(.2, 1.4, .4, 1)",
}: GlassNavbarProps) {
  const style: Vars = { "--duration": duration, "--easing": easing };
  return (
    <nav className={styles.nav} style={style} aria-label="glass nav">
      <span className={styles.pill} aria-hidden="true" />
      {LINKS.map((label) => (
        <a key={label} className={styles.link} href="#">
          {label}
        </a>
      ))}
    </nav>
  );
}