Back to CSS Navbars CSS Navbar with Underline Hover Animation CSS + JS
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HTML 
<section class="nb-und" aria-label="CSS navbar with underline hover animation demo">
  <nav aria-label="Primary">
    <div class="nav-inner">
      <a href="#" class="brand">Thesis</a>

      <div class="nav-links-wrap" data-nb-und-wrap>
        <div class="ink-line" data-nb-und-line aria-hidden="true"></div>
        <div class="ink-line-static" data-nb-und-static aria-hidden="true"></div>

        <ul class="nav-links" data-nb-und-nav>
          <li><a href="#" class="active"><span>Studio</span></a></li>
          <li><a href="#"><span>Work</span></a></li>
          <li><a href="#"><span>Writing</span></a></li>
          <li><a href="#"><span>Process</span></a></li>
          <li><a href="#"><span>Archive</span></a></li>
          <li><a href="#"><span>Contact</span></a></li>
        </ul>
      </div>

      <div class="nav-spacer"></div>

      <div class="nav-end">
        <a href="#">Index</a>
        <div class="nav-end-dot" aria-hidden="true"></div>
        <a href="#">RSS</a>
        <div class="nav-end-dot" aria-hidden="true"></div>
        <button class="btn-nav" type="button">Inquire</button>
      </div>
    </div>
  </nav>

  <div class="page">
    <div class="hero">
      <div class="hero-left">
        <h1>The art of<br>the <em>quiet</em><br>hover.</h1>
        <p>Three distinct CSS underline animation techniques — each achieving elegance through restraint. The navbar above uses a magnetic sliding ink line that follows your cursor. Below, explore every method.</p>
      </div>
      <div class="hero-right">
        <p>"Typography is a <strong>silent conversation</strong> — the best underlines join it without interrupting. Hover the navigation above and each demo below to see them in motion."</p>
      </div>
    </div>

    <div class="section-rule"></div>

    <section class="section">
      <div class="variant-label">
        <span class="variant-num">01</span>
        <div class="variant-info">
          <h3>Magnetic Sliding Line — Single Global Rail</h3>
          <p>One line glides beneath the entire nav, tracking the hovered link. Active item uses a static accent-colored line.</p>
        </div>
      </div>
      <div class="demo-nav">
        <div class="nav-links-wrap demo-wrap" data-nb-und-demo-wrap>
          <div class="ink-line" data-nb-und-demo-line aria-hidden="true"></div>
          <div class="ink-line-static" data-nb-und-demo-static aria-hidden="true"></div>
          <ul class="nav-links" data-nb-und-demo-nav>
            <li><a href="#" class="active"><span>Objects</span></a></li>
            <li><a href="#"><span>Spaces</span></a></li>
            <li><a href="#"><span>Systems</span></a></li>
            <li><a href="#"><span>Texts</span></a></li>
            <li><a href="#"><span>People</span></a></li>
          </ul>
        </div>
      </div>
      <p class="code-note">
        One <code>.ink-line</code> element is positioned with JS using <code>getBoundingClientRect()</code> on each hover target.
        CSS <code>transition: left, width</code> with <code>cubic-bezier(0.25,1,0.5,1)</code> creates the magnetic feel.
        The static <code>.ink-line-static</code> marks the active item in accent red.
      </p>
    </section>

    <div class="section-rule"></div>

    <section class="section">
      <div class="variant-label">
        <span class="variant-num">02</span>
        <div class="variant-info">
          <h3>Center-Bloom — Per-Link <code>::after</code> Pseudo-Element</h3>
          <p>Each link owns its underline. On hover, it expands from the center outward — no JavaScript needed at all.</p>
        </div>
      </div>
      <div class="demo-nav">
        <ul class="nav-links-v2">
          <li><a href="#" class="active">Foundations</a></li>
          <li><a href="#">Components</a></li>
          <li><a href="#">Patterns</a></li>
          <li><a href="#">Motion</a></li>
          <li><a href="#">Tokens</a></li>
        </ul>
      </div>
      <p class="code-note">
        CSS only. Each <code>a::after</code> starts at <code>left: 50%; right: 50%</code> (zero width, centered).
        On <code>:hover</code>, <code>left</code> and <code>right</code> both animate to the padding value — blooming outward symmetrically.
      </p>
    </section>

    <div class="section-rule"></div>

    <section class="section">
      <div class="variant-label">
        <span class="variant-num">03</span>
        <div class="variant-info">
          <h3>Left-Wipe — Directional Reveal</h3>
          <p>The underline sweeps in from the left, anchored to the link's left edge. Clean, directional, editorial.</p>
        </div>
      </div>
      <div class="demo-nav">
        <ul class="nav-links-v3">
          <li><a href="#" class="active">Editorial</a></li>
          <li><a href="#">Research</a></li>
          <li><a href="#">Narrative</a></li>
          <li><a href="#">Margins</a></li>
          <li><a href="#">Colophon</a></li>
        </ul>
      </div>
      <p class="code-note">
        CSS only. <code>a::before</code> starts at <code>left: 50%; right: 50%</code> and transitions to <code>left: 1.1rem; right: 1.1rem</code>.
        The asymmetric easing of <code>left</code> gives it the wipe directionality.
      </p>
    </section>

    <div class="section-rule"></div>

    <div class="alphabet-demo">
      <p class="alpha-label">Every link, same principle — hover any letter</p>
      <div class="alpha-links" data-nb-und-alpha></div>
    </div>

    <div class="section-rule"></div>

    <div class="showcase">
      <div class="showcase-item">
        <span class="showcase-title">Clarity</span>
        <div class="showcase-right">
          <span class="showcase-meta">Principle 01</span>
          <span class="showcase-arrow" aria-hidden="true">→</span>
        </div>
      </div>
      <div class="showcase-item">
        <span class="showcase-title">Restraint</span>
        <div class="showcase-right">
          <span class="showcase-meta">Principle 02</span>
          <span class="showcase-arrow" aria-hidden="true">→</span>
        </div>
      </div>
      <div class="showcase-item">
        <span class="showcase-title">Intention</span>
        <div class="showcase-right">
          <span class="showcase-meta">Principle 03</span>
          <span class="showcase-arrow" aria-hidden="true">→</span>
        </div>
      </div>
      <div class="showcase-item">
        <span class="showcase-title">Motion</span>
        <div class="showcase-right">
          <span class="showcase-meta">Principle 04</span>
          <span class="showcase-arrow" aria-hidden="true">→</span>
        </div>
      </div>
    </div>
  </div>
</section>
CSS 
/* ─── 08 Thesis — CSS navbar underline hover animation UI ─────── */
@import url('https://fonts.googleapis.com/css2?family=Libre+Baskerville:ital,wght@0,400;0,700;1,400&family=Instrument+Sans:ital,wght@0,400;0,500;0,600;1,400&display=swap');

.nb-und {
  --nb-und-paper: #f8f6f1;
  --nb-und-ink: #1a1916;
  --nb-und-ink-2: #6b6760;
  --nb-und-ink-3: #b5b2ac;
  --nb-und-rule: #e0ddd6;
  --nb-und-red: #c93a24;
  --nb-und-nav-h: 70px;

  position: relative;
  width: 100%;
  min-height: 1600px;
  background: var(--nb-und-paper);
  color: var(--nb-und-ink);
  font-family: 'Instrument Sans', sans-serif;
  overflow: clip;
  box-sizing: border-box;
}
.nb-und *, .nb-und *::before, .nb-und *::after { box-sizing: border-box; margin: 0; padding: 0; }

.nb-und nav { position: absolute; top: 0; left: 0; right: 0; z-index: 100; height: var(--nb-und-nav-h); background: var(--nb-und-paper); border-bottom: 1px solid var(--nb-und-rule); }
.nb-und .nav-inner { max-width: 1440px; margin: 0 auto; height: 100%; display: flex; align-items: center; padding: 0 3rem; }
.nb-und .brand { font-family: 'Libre Baskerville', serif; font-size: 1.2rem; font-weight: 700; letter-spacing: -0.01em; color: var(--nb-und-ink); text-decoration: none; flex-shrink: 0; margin-right: 4rem; }

.nb-und .nav-links-wrap { flex: 1; position: relative; display: flex; align-items: center; }
.nb-und .nav-links { display: flex; align-items: center; list-style: none; gap: 0; }
.nb-und .ink-line { position: absolute; bottom: -1px; height: 1.5px; background: var(--nb-und-ink); transition: left 0.38s cubic-bezier(0.25, 1, 0.5, 1), width 0.38s cubic-bezier(0.25, 1, 0.5, 1), opacity 0.25s; pointer-events: none; opacity: 0; }
.nb-und .ink-line.visible { opacity: 1; }
.nb-und .ink-line-static { position: absolute; bottom: -1px; height: 1.5px; background: var(--nb-und-red); pointer-events: none; transition: left 0.4s cubic-bezier(0.25, 1, 0.5, 1), width 0.4s; }

.nb-und .nav-links a { display: flex; align-items: center; font-size: 0.8rem; font-weight: 500; letter-spacing: 0.04em; color: var(--nb-und-ink-2); text-decoration: none; padding: 0 1.1rem; height: var(--nb-und-nav-h); transition: color 0.22s; position: relative; white-space: nowrap; }
.nb-und .nav-links a:hover { color: var(--nb-und-ink); }
.nb-und .nav-links a.active { color: var(--nb-und-ink); }
.nb-und .nav-links a span { display: inline-block; transition: letter-spacing 0.35s cubic-bezier(0.25, 1, 0.5, 1); }
.nb-und .nav-links a:hover span { letter-spacing: 0.09em; }
.nb-und .nav-links a.active span { letter-spacing: 0.02em; }

/* Variant 2 — center-bloom (pure CSS) */
.nb-und .nav-links-v2 { display: flex; align-items: center; list-style: none; gap: 0; }
.nb-und .nav-links-v2 a { display: flex; align-items: center; justify-content: center; font-size: 0.8rem; font-weight: 500; letter-spacing: 0.04em; color: var(--nb-und-ink-2); text-decoration: none; padding: 0 1.1rem; height: var(--nb-und-nav-h); position: relative; white-space: nowrap; transition: color 0.22s; }
.nb-und .nav-links-v2 a:hover { color: var(--nb-und-ink); }
.nb-und .nav-links-v2 a.active { color: var(--nb-und-ink); }
.nb-und .nav-links-v2 a::after { content: ''; position: absolute; bottom: 0; left: 50%; right: 50%; height: 1.5px; background: var(--nb-und-ink); transition: left 0.35s cubic-bezier(0.25, 1, 0.5, 1), right 0.35s cubic-bezier(0.25, 1, 0.5, 1); }
.nb-und .nav-links-v2 a.active::after { background: var(--nb-und-red); left: 1.1rem; right: 1.1rem; }
.nb-und .nav-links-v2 a:hover::after { left: 1.1rem; right: 1.1rem; }

/* Variant 3 — left-wipe */
.nb-und .nav-links-v3 { display: flex; align-items: center; list-style: none; gap: 0; }
.nb-und .nav-links-v3 a { display: flex; align-items: center; height: var(--nb-und-nav-h); padding: 0 1.1rem; text-decoration: none; white-space: nowrap; position: relative; overflow: hidden; font-size: 0.8rem; font-weight: 500; letter-spacing: 0.04em; color: var(--nb-und-ink-2); transition: color 0.22s; }
.nb-und .nav-links-v3 a:hover, .nb-und .nav-links-v3 a.active { color: var(--nb-und-ink); }
.nb-und .nav-links-v3 a::before { content: ''; position: absolute; bottom: 0; left: 50%; right: 50%; height: 1.5px; background: var(--nb-und-ink); transition: left 0.3s ease, right 0.3s ease; }
.nb-und .nav-links-v3 a:hover::before { left: 1.1rem; right: 1.1rem; }
.nb-und .nav-links-v3 a.active::before { left: 1.1rem; right: 1.1rem; background: var(--nb-und-red); }

.nb-und .nav-spacer { flex: 1; }
.nb-und .nav-end { display: flex; align-items: center; gap: 1.5rem; flex-shrink: 0; }
.nb-und .nav-end a { font-size: 0.78rem; font-weight: 500; letter-spacing: 0.04em; color: var(--nb-und-ink-2); text-decoration: none; transition: color 0.2s; position: relative; }
.nb-und .nav-end a::after { content: ''; position: absolute; bottom: -2px; left: 50%; right: 50%; height: 1px; background: var(--nb-und-ink); transition: left 0.3s ease, right 0.3s ease; }
.nb-und .nav-end a:hover { color: var(--nb-und-ink); }
.nb-und .nav-end a:hover::after { left: 0; right: 0; }
.nb-und .nav-end-dot { width: 3px; height: 3px; border-radius: 50%; background: var(--nb-und-rule); }
.nb-und .btn-nav { font-family: 'Instrument Sans', sans-serif; font-size: 0.72rem; font-weight: 600; letter-spacing: 0.08em; color: var(--nb-und-paper); background: var(--nb-und-ink); border: none; padding: 8px 18px; border-radius: 2px; cursor: pointer; transition: background 0.2s; }
.nb-und .btn-nav:hover { background: var(--nb-und-red); }

.nb-und .page { padding-top: var(--nb-und-nav-h); }

.nb-und .hero { padding: 6rem 3rem 4rem; max-width: 1440px; margin: 0 auto; display: grid; grid-template-columns: 1fr 1fr; gap: 6rem; align-items: end; }
.nb-und .hero-left h1 { font-family: 'Libre Baskerville', serif; font-size: clamp(3rem, 5vw, 5.5rem); font-weight: 700; letter-spacing: -0.03em; line-height: 1.08; color: var(--nb-und-ink); margin-bottom: 1.5rem; }
.nb-und .hero-left h1 em { font-style: italic; font-weight: 400; color: var(--nb-und-red); }
.nb-und .hero-left p { font-size: 1rem; color: var(--nb-und-ink-2); line-height: 1.7; max-width: 44ch; }
.nb-und .hero-right { padding-bottom: 1rem; }
.nb-und .hero-right p { font-family: 'Libre Baskerville', serif; font-size: 1.3rem; font-style: italic; font-weight: 400; color: var(--nb-und-ink-2); line-height: 1.6; max-width: 36ch; }
.nb-und .hero-right p strong { color: var(--nb-und-ink); font-style: normal; font-weight: 700; }

.nb-und .section-rule { height: 1px; background: var(--nb-und-rule); margin: 0 3rem; }
.nb-und .section { padding: 5rem 3rem; max-width: 1440px; margin: 0 auto; }
.nb-und .variant-label { display: flex; align-items: center; gap: 1rem; margin-bottom: 2rem; }
.nb-und .variant-num { font-family: 'Libre Baskerville', serif; font-size: 3rem; font-weight: 400; color: var(--nb-und-rule); line-height: 1; }
.nb-und .variant-info h3 { font-size: 0.88rem; font-weight: 600; color: var(--nb-und-ink); letter-spacing: 0.02em; margin-bottom: 3px; }
.nb-und .variant-info p { font-size: 0.78rem; color: var(--nb-und-ink-2); line-height: 1.5; }

.nb-und .demo-nav { border: 1px solid var(--nb-und-rule); border-radius: 4px; background: var(--nb-und-paper); height: 60px; display: flex; align-items: center; padding: 0 2rem; position: relative; margin-bottom: 1.5rem; overflow: hidden; }
.nb-und .demo-wrap { position: relative; display: flex; align-items: center; }
.nb-und .code-note { font-family: 'Instrument Sans', monospace; font-size: 0.72rem; color: var(--nb-und-ink-3); line-height: 1.7; background: #f2f0ea; border-left: 2px solid var(--nb-und-rule); padding: 0.75rem 1rem; border-radius: 0 3px 3px 0; margin-bottom: 3rem; }
.nb-und .code-note code { font-family: monospace; color: var(--nb-und-red); font-size: 0.7rem; }

.nb-und .alphabet-demo { margin: 4rem 3rem; padding: 3rem; border: 1px solid var(--nb-und-rule); border-radius: 4px; text-align: center; }
.nb-und .alpha-label { font-size: 0.62rem; letter-spacing: 0.15em; text-transform: uppercase; color: var(--nb-und-ink-3); margin-bottom: 2rem; }
.nb-und .alpha-links { display: flex; align-items: center; justify-content: center; gap: 0; flex-wrap: wrap; }
.nb-und .alpha-links a { display: inline-flex; align-items: center; justify-content: center; width: 40px; height: 40px; font-family: 'Libre Baskerville', serif; font-size: 1rem; color: var(--nb-und-ink-3); text-decoration: none; position: relative; transition: color 0.2s; border-radius: 4px; }
.nb-und .alpha-links a::after { content: ''; position: absolute; bottom: 4px; left: 50%; right: 50%; height: 1px; background: var(--nb-und-ink); transition: left 0.3s ease, right 0.3s ease; }
.nb-und .alpha-links a:hover { color: var(--nb-und-ink); }
.nb-und .alpha-links a:hover::after { left: 8px; right: 8px; }

.nb-und .showcase { padding: 5rem 3rem; border-top: 1px solid var(--nb-und-rule); max-width: 1440px; margin: 0 auto; display: flex; flex-direction: column; gap: 0; }
.nb-und .showcase-item { display: flex; align-items: center; justify-content: space-between; padding: 2rem 0; border-bottom: 1px solid var(--nb-und-rule); cursor: pointer; overflow: hidden; position: relative; }
.nb-und .showcase-title { font-family: 'Libre Baskerville', serif; font-size: clamp(2rem, 4vw, 4rem); font-weight: 400; color: var(--nb-und-ink); line-height: 1; position: relative; display: inline-block; transition: color 0.2s; }
.nb-und .showcase-title::after { content: ''; position: absolute; bottom: 4px; left: 0; right: 100%; height: 2px; background: var(--nb-und-red); transition: right 0.5s cubic-bezier(0.25, 1, 0.5, 1); }
.nb-und .showcase-item:hover .showcase-title::after { right: 0; }
.nb-und .showcase-item:hover .showcase-title { color: var(--nb-und-red); }
.nb-und .showcase-right { display: flex; align-items: center; gap: 1rem; }
.nb-und .showcase-meta { font-size: 0.72rem; font-weight: 500; letter-spacing: 0.1em; text-transform: uppercase; color: var(--nb-und-ink-3); }
.nb-und .showcase-arrow { font-size: 1.5rem; color: var(--nb-und-ink-3); transform: translateX(-8px); transition: transform 0.3s ease, color 0.2s; }
.nb-und .showcase-item:hover .showcase-arrow { transform: translateX(0); color: var(--nb-und-red); }

@media (max-width: 900px) {
  .nb-und .hero { grid-template-columns: 1fr; gap: 2rem; padding: 3rem 1.5rem 2rem; }
  .nb-und .nav-end a, .nb-und .nav-end-dot { display: none; }
  .nb-und .section { padding: 3rem 1.5rem; }
  .nb-und .alphabet-demo { margin: 2rem 1.5rem; padding: 2rem 1rem; }
  .nb-und .showcase { padding: 3rem 1.5rem; }
  .nb-und .demo-nav { padding: 0 1rem; }
  .nb-und nav .nav-inner { padding: 0 1.5rem; }
}
@media (prefers-reduced-motion: reduce) {
  .nb-und * { transition: none !important; }
}
JS 
(() => {
  // Scoped magnetic-line wiring. Two instances of the magnetic line
  // pattern run on the page (the main top nav + the demo nav in
  // variant 01). Each is independently bound to its wrapper + nav
  // + line + static-line via data-* attributes — no document.getElementById,
  // no shared state, multiple instances coexist safely.
  const root = document.querySelector('.nb-und');
  if (!root) return;

  function setupMagneticLine(navEl, wrapper, line, staticLine) {
    if (!navEl || !wrapper || !line || !staticLine) return;
    const links = navEl.querySelectorAll('a');

    function positionLine(el, targetLine, useAccent) {
      const wRect = wrapper.getBoundingClientRect();
      const rect = el.getBoundingClientRect();
      targetLine.style.left = (rect.left - wRect.left) + 'px';
      targetLine.style.width = rect.width + 'px';
      if (useAccent) targetLine.style.background = 'var(--nb-und-red)';
    }

    const active = navEl.querySelector('a.active');
    if (active) {
      requestAnimationFrame(() => positionLine(active, staticLine, true));
    }

    links.forEach((a) => {
      a.addEventListener('mouseenter', () => {
        positionLine(a, line);
        line.classList.add('visible');
      });
      a.addEventListener('click', (e) => {
        e.preventDefault();
        links.forEach((l) => l.classList.remove('active'));
        a.classList.add('active');
        positionLine(a, staticLine, true);
      });
    });
    wrapper.addEventListener('mouseleave', () => {
      line.classList.remove('visible');
    });
  }

  // Main top nav
  setupMagneticLine(
    root.querySelector('[data-nb-und-nav]'),
    root.querySelector('[data-nb-und-wrap]'),
    root.querySelector('[data-nb-und-line]'),
    root.querySelector('[data-nb-und-static]'),
  );

  // Demo 1 (the in-page variant showcase)
  setupMagneticLine(
    root.querySelector('[data-nb-und-demo-nav]'),
    root.querySelector('[data-nb-und-demo-wrap]'),
    root.querySelector('[data-nb-und-demo-line]'),
    root.querySelector('[data-nb-und-demo-static]'),
  );

  // Variant 2 / 3 click-to-activate (pure CSS hover; this just keeps the
  // active state in sync after a click).
  root.querySelectorAll('.nav-links-v2 a, .nav-links-v3 a').forEach((a) => {
    a.addEventListener('click', (e) => {
      e.preventDefault();
      const siblings = a.closest('ul').querySelectorAll('a');
      siblings.forEach((s) => s.classList.remove('active'));
      a.classList.add('active');
    });
  });

  // Alphabet ticker — 26 links built once.
  const alpha = root.querySelector('[data-nb-und-alpha]');
  if (alpha && alpha.childElementCount === 0) {
    'ABCDEFGHIJKLMNOPQRSTUVWXYZ'.split('').forEach((ch) => {
      const a = document.createElement('a');
      a.href = '#';
      a.textContent = ch;
      a.addEventListener('click', (e) => e.preventDefault());
      alpha.appendChild(a);
    });
  }
})();