如何修复导航栏悬停问题 CSS

我正在引导程序 4 中的导航栏上工作。当我将鼠标悬停在导航链接上时遇到问题。我为导航链接在悬停时添加了边框底部。但是当悬停时，整个导航栏都会移动。我已经粘贴了到目前为止我所做的。

<nav class="navbar navbar-expand-lg navbar-dark bg-dark">
  <a class="navbar-brand" href="#">
    <img src="#" />
  </a>
  <button class="navbar-toggler" type="button" data-toggle="collapse" data-target="#navbarSupportedContent" aria-controls="navbarSupportedContent" aria-expanded="false" aria-label="Toggle navigation">
    <span class="navbar-toggler-icon"></span>
  </button>

  <div class="collapse navbar-collapse" id="navbarSupportedContent">
    <ul class="navbar-nav mr-auto">
      <li class="nav-item active">
        <a class="nav-link" href="#">First item</a>
      </li>
      <li class="nav-item">
        <a class="nav-link" href="#">Second Item</a>
      </li>
      <li class="nav-item dropdown">
        <a class="nav-link dropdown-toggle" href="#" id="navbarDropdown" role="button" data-toggle="dropdown" aria-haspopup="true" aria-expanded="false">
          Dropdown
        </a>
        <div class="dropdown-menu" aria-labelledby="navbarDropdown">
          <a class="dropdown-item" href="#">Action</a>
          <a class="dropdown-item" href="#">Another action</a>
          <div class="dropdown-divider"></div>
          <a class="dropdown-item" href="#">Something else here</a>
        </div>
      </li>
    </ul>
    <div class="my-2 my-lg-0">
    </div>
  </div>
</nav>

<style>
.navbar-dark .navbar-nav .nav-link:hover, 
.navbar-dark .navbar-nav .nav-link:focus {
  color: rgba(255, 255, 255, 0.75);
  border-bottom: 2px solid #fff;
}

</style>