Sticky Search Header

<header class="nuda-sticksrch">
  <span>Components</span>
  <div class="nuda-sticksrch__field">
    <svg viewBox="0 0 24 24" fill="none" stroke="currentColor"
         stroke-width="2" stroke-linecap="round" stroke-linejoin="round">
      <circle cx="11" cy="11" r="7" />
      <path d="m21 21-4.3-4.3" />
    </svg>
    <input placeholder="Filter…" />
  </div>
</header>

// Add .is-stuck once the header crosses a threshold
const header = document.querySelector('.nuda-sticksrch');
const onScroll = () => {
  header.classList.toggle('is-stuck', window.scrollY > 60);
};
window.addEventListener('scroll', onScroll, { passive: true });
onScroll();

.nuda-sticksrch {
  display: flex;
  align-items: center;
  justify-content: space-between;
  gap: 12px;
  padding: 10px 14px;
  background: rgba(17,17,20,.5);
  border: 1px solid rgba(255,255,255,.06);
  border-radius: 12px;
  width: 100%;
  max-width: 280px;
  transition: background .3s,backdrop-filter .3s,box-shadow .3s,padding .3s;
}

.nuda-sticksrch.is-stuck {
  background: rgba(17,17,20,.85);
  backdrop-filter: blur(14px);
  box-shadow: 0 4px 16px -8px rgba(0,0,0,.5);
  padding: 8px 14px;
}

.nuda-sticksrch > span {
  color: #fafafa;
  font-size: 12px;
  font-weight: 600;
}

.nuda-sticksrch__field {
  display: flex;
  align-items: center;
  gap: 6px;
  padding: 5px 10px;
  background: rgba(0,0,0,.3);
  border: 1px solid rgba(255,255,255,.06);
  border-radius: 8px;
  width: 120px;
  transition: width .35s cubic-bezier(.16,1,.3,1);
}

.nuda-sticksrch__field:focus-within {
  width: 160px;
  border-color: #e4ff54;
}

.nuda-sticksrch__field svg {
  width: 11px;
  height: 11px;
  color: #63636e;
  flex-shrink: 0;
}

.nuda-sticksrch__field input {
  flex: 1;
  min-width: 0;
  background: transparent;
  border: 0;
  outline: none;
  color: #fafafa;
  font-size: 11px;
}

.nuda-sticksrch__field input::placeholder {
  color: #63636e;
}