02Underline nav

<main class="stage">
  <nav class="navtrust">
    <span class="navtrust__highlight" aria-hidden="true"></span>
    <span class="navtrust__tab">Home</span>
    <span class="navtrust__tab">Features</span>
    <span class="navtrust__tab">Pricing</span>
    <span class="navtrust__underline" aria-hidden="true"></span>
  </nav>
</main>

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

$duration: 3s;          // 세 칸을 도는 한 바퀴 — 2s 로프($dur-loop)보다 정거장이 많아 별도 토큰(합치지 않는다, blog-design 규칙 2)
$easing: $ease-out;
$color: $subject-blue;

$trust-graytint: #f1f5f9;
$trust-ink:      $subject-ink;
$trust-blue:     $subject-blue;

@include stage($trust-graytint);

// 탭 3개 — 폭을 고정(flex:0 0 auto)해 인디케이터 translateX 이동량과 어긋나지 않는다 (BD19). 320px 안에 들어가도록 전체 폭을 284px 로 미리 잡는다
$tab-w: 92px;
$tab-h: 48px;
$underline-w: 28px;
$underline-offset: 32px; // ($tab-w - $underline-w) / 2, 나눗셈 없이 상수로

.navtrust {
  position: relative;
  box-sizing: border-box;
  display: flex;
  align-items: center;
  width: $tab-w * 3 + $sp-2;
  height: $tab-h;
  padding: 0 $sp-1;
  border-radius: $r-pill;
  background: $stage-paper;
  box-shadow: 0 10px 22px rgba($trust-ink, .08);
}
.navtrust__highlight {
  position: absolute;
  left: $sp-1;
  top: 2px;
  width: $tab-w - 4px;
  height: $tab-h - 4px;
  border-radius: $r-control;
  background: rgba($trust-blue, .14);
  animation: slideTab $duration $easing infinite;
}
.navtrust__tab {
  position: relative;
  z-index: 1;
  flex: 0 0 $tab-w;
  text-align: center;
  color: $trust-ink;
  font-weight: 600; font-size: clamp(11px, 3vw, 13px); line-height: 1;
  font-family: inherit;
}
.navtrust__underline {
  position: absolute;
  bottom: -$sp-2;
  left: 0;
  width: $underline-w;
  height: 3px;
  border-radius: $r-xs;
  background: $trust-blue;
  transform: translateX($underline-offset);
  animation: slideUnderline $duration $easing infinite;
}

// 데모: 하이라이트 블록(넓은 면적)과 밑줄(얇은 신호선)이 같은 박자로 세 칸을 순서대로 돈다
@keyframes slideTab {
  0%, 22%  { transform: translateX(0); }
  33%, 55% { transform: translateX($tab-w); }
  66%, 88% { transform: translateX($tab-w * 2); }
  100%     { transform: translateX(0); }
}
@keyframes slideUnderline {
  0%, 22%  { transform: translateX($underline-offset); }
  33%, 55% { transform: translateX($tab-w + $underline-offset); }
  66%, 88% { transform: translateX($tab-w * 2 + $underline-offset); }
  100%     { transform: translateX($underline-offset); }
}

@media (prefers-reduced-motion: reduce) {
  .navtrust__highlight, .navtrust__underline { animation: none !important; }
  .navtrust__highlight { transform: translateX(0); }
  .navtrust__underline { transform: translateX($underline-offset); }
}

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

.stage {
  box-sizing: border-box;
  min-height: 100vh;
  display: grid;
  place-items: center;
  margin: 0;
  background: #f1f5f9;
  font-family: -apple-system, "Segoe UI", "Noto Sans KR", sans-serif;
  padding: clamp(8px, 4vw, 24px);
}

.navtrust {
  position: relative;
  box-sizing: border-box;
  display: flex;
  align-items: center;
  width: 284px;
  height: 48px;
  padding: 0 4px;
  border-radius: 999px;
  background: #ffffff;
  box-shadow: 0 10px 22px rgba(23, 20, 26, 0.08);
}

.navtrust__highlight {
  position: absolute;
  left: 4px;
  top: 2px;
  width: 88px;
  height: 44px;
  border-radius: 12px;
  background: rgba(47, 109, 246, 0.14);
  animation: slideTab 3s ease-out infinite;
}

.navtrust__tab {
  position: relative;
  z-index: 1;
  flex: 0 0 92px;
  text-align: center;
  color: #17141a;
  font-weight: 600;
  font-size: clamp(11px, 3vw, 13px);
  line-height: 1;
  font-family: inherit;
}

.navtrust__underline {
  position: absolute;
  bottom: -8px;
  left: 0;
  width: 28px;
  height: 3px;
  border-radius: 4px;
  background: #2f6df6;
  transform: translateX(32px);
  animation: slideUnderline 3s ease-out infinite;
}

@keyframes slideTab {
  0%, 22% {
    transform: translateX(0);
  }
  33%, 55% {
    transform: translateX(92px);
  }
  66%, 88% {
    transform: translateX(184px);
  }
  100% {
    transform: translateX(0);
  }
}
@keyframes slideUnderline {
  0%, 22% {
    transform: translateX(32px);
  }
  33%, 55% {
    transform: translateX(124px);
  }
  66%, 88% {
    transform: translateX(216px);
  }
  100% {
    transform: translateX(32px);
  }
}
@media (prefers-reduced-motion: reduce) {
  .navtrust__highlight, .navtrust__underline {
    animation: none !important;
  }
  .navtrust__highlight {
    transform: translateX(0);
  }
  .navtrust__underline {
    transform: translateX(32px);
  }
}

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

export type NavTrustProps = {
  tabs?: string[];
  duration?: number;
  easing?: string;
  color?: string;
};

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

export default function NavTrust({
  tabs = ["홈", "기능", "요금제"],
  duration = 3000,
  easing = "ease-out",
  color = "#2f6df6",
}: NavTrustProps) {
  const vars: Vars = { "--duration": `${duration}ms`, "--easing": easing, "--color": color };
  return (
    <nav className={styles.navtrust} style={vars}>
      <span className={styles.highlight} aria-hidden="true" />
      {tabs.map((t) => (
        <span key={t} className={styles.tab}>{t}</span>
      ))}
      <span className={styles.underline} aria-hidden="true" />
    </nav>
  );
}