如何在导航栏中只显示一个箭头？

<nav class="navbar">
  <div class="nav-item">
    <span class="arrow"></span>
  </div>
</nav>

.navbar {
  display: flex;
  justify-content: center;
  align-items: center;
  background-color: #f1f1f1;
  padding: 10px;
}

.nav-item {
  position: relative;
  cursor: pointer;
}

.arrow {
  border: solid black;
  border-width: 0 2px 2px 0;
  display: inline-block;
  padding: 3px;
  transform: rotate(45deg);
  transition: transform 0.3s ease;
}

.nav-item.expanded .arrow {
  transform: rotate(-135deg);
}

document.querySelector('.nav-item').addEventListener('click', function() {
  this.classList.toggle('expanded');
});