如何为我的下拉菜单文本和中心下拉菜单文本的导航栏文本重复下划线CSS？

Question

问题1

当我将鼠标悬停在下拉菜单中的导航栏文字上时，我会在框底部显示下划线。但是，我希望在导航栏下拉菜单文本中执行该过程。当用户将鼠标悬停在下拉菜单文本上而不是位于文本底部的下划线时，它位于下拉菜单框的底部。我怎样才能做到这一点？

问题2

如何让导航栏下拉菜单文本以便网页在中心一个接一个地显示？

这是我的codepen，其中包含所有html和CSS。

HTML BELOW

<nav class="navbar navbar-default">
    <div class="container-fluid">
        <div class="navbar-header">
            <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
                <span class="sr-only">Toggle navigation</span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
                <span class="icon-bar"></span>
            </button>
            <a class="navbar-brand" href="#"><img src="http://placehold.it/60x60" alt="Your Brand Name"></a>
        </div>

        <!-- Collect the nav links, forms, and other content for toggling -->
        <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
            <ul class="nav navbar-nav">
                    <li><a href="#">Home</a>
                    </li>
                    <li class="dropdown">
                        <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="true">About Me <span class="caret"></span></a>
                        <ul class="dropdown-menu">
                            <li><a href="#">Action</a>
                            </li>
                            <li><a href="#">Another action</a>
                            </li>
                            <li><a href="#">Something else here</a>
                            </li>
                            <li role="separator" class="divider"></li>
                            <li><a href="#">Separated link</a>
                            </li>
                            <li role="separator" class="divider"></li>
                            <li><a href="#">One more separated link</a>
                            </li>
                        </ul>
                    </li>
                    <li class="dropdown">
                        <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Units <span class="caret"></span></a>
                        <ul class="dropdown-menu">
                            <li><a href="#">Action</a>
                            </li>
                            <li><a href="#">Another action</a>
                            </li>
                            <li><a href="#">Something else here</a>
                            </li>
                            <li role="separator" class="divider"></li>
                            <li><a href="#">Separated link</a>
                            </li>
                            <li role="separator" class="divider"></li>
                            <li><a href="#">One more separated link</a>
                            </li>
                        </ul>
                    </li>
                    <li><a href="#">Clients</a>
                    </li>
                    <li><a href="#contact-me">Contact Me</a>
                    </li>
                </ul>
              </div><!-- /.navbar-collapse -->
            </div><!-- /.container-fluid -->
</nav>

Answer 1

将display: block; position: relative;添加到下拉列表li和a＆＃39}。该边界基于绝对定位的元素，并且绝对定位的元素相对于最接近的非静态定位的祖先定位。将它们设置为阻止将确保它们按照自己的方式排列，并且您已应用于父级的text-align: center将起作用。

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body {
  margin: 0;
  padding: 0;
}

.navbar.navbar-default {
  background-color: #4D5061;
  height: 10vh;
}

.navbar.navbar-default ul {
  list-style-type: none;
  text-align: center;
}

.navbar.navbar-default ul li {
  display: inline-block;
}

.dropdown .dropdown-menu {
  background-color: #4D5061;
}

.dropdown .dropdown-menu a {
  color: white;
}

.navbar.navbar-default ul li a {
  display: inline-block;
  padding: 3.5vh 8px 4px;
  color: white;
  text-decoration: none;
  font-size: 14pt;
  font-family: 'Roboto', sans-serif;
}

.navbar.navbar-default ul li:after {
  content: '';
  position: absolute;
  right: 50%;
  bottom: 0;
  left: 50%;
  height: 3px;
  background-color: red;
  border-radius: 9px;
  transition: all .2s;
}

.navbar.navbar-default ul li a:hover {
  color: red;
}

.nav.navbar-nav,
.nav.navbar-nav>li {
  float: none;
}

.navbar.navbar-default ul li:hover:after {
  right: 0;
  left: 0;
}

a:hover {
  color: red;
  text-decoration: none;
}

#logo {
  padding-top: 2vh;
  padding-left: 20px;
  float: left;
}

section {
  position: relative;
}

.section1 {
  height: 90vh;
  background-color: #FFFFFF;
  text-align: center;
}

.section2 {
  height: 95vh;
  background-color: #A59E8C;
  text-align: center;
  color: white;
}

.contact_section {
  height: 93vh;
  background-color: grey;
}

.fa-angle-down {
  color: #4D5061;
  position: absolute;
  bottom: 0px;
}

footer {
  height: 5vh;
}

.navbar.navbar-default ul.dropdown-menu li,
.navbar.navbar-default ul.dropdown-menu li a {
  position: relative;
  display: block;
}

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<!DOCTYPE html>
<html lang="en">

<html>

<head>
  <title>Liam Docherty | London Web Developer &amp; GFX designer</title>
  <link rel="stylesheet" href="https://cdnjs.cloudflare.com/ajax/libs/font-awesome/4.7.0/css/font-awesome.min.css">
  <link rel="stylesheet" href="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/css/bootstrap.min.css">
</head>

<body>
  <nav class="navbar navbar-default">
    <div class="container-fluid">
      <!-- Brand and toggle get grouped for better mobile display -->
      <div class="navbar-header">
        <button type="button" class="navbar-toggle collapsed" data-toggle="collapse" data-target="#bs-example-navbar-collapse-1" aria-expanded="false">
                            <span class="sr-only">Toggle navigation</span>
                            <span class="icon-bar"></span>
                            <span class="icon-bar"></span>
                            <span class="icon-bar"></span>
                        </button>
        <a class="navbar-brand" href="#"><img src="http://placehold.it/60x60" alt="Your Brand Name"></a>
      </div>

      <!-- Collect the nav links, forms, and other content for toggling -->
      <div class="collapse navbar-collapse" id="bs-example-navbar-collapse-1">
        <ul class="nav navbar-nav">
          <li><a href="#">Home</a>
          </li>
          <li class="dropdown">
            <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="true">About Me <span class="caret"></span></a>
            <ul class="dropdown-menu">
              <li><a href="#">Action</a>
              </li>
              <li><a href="#">Another action</a>
              </li>
              <li><a href="#">Something else here</a>
              </li>
              <li role="separator" class="divider"></li>
              <li><a href="#">Separated link</a>
              </li>
              <li role="separator" class="divider"></li>
              <li><a href="#">One more separated link</a>
              </li>
            </ul>
          </li>
          <li class="dropdown">
            <a href="#" class="dropdown-toggle" data-toggle="dropdown" role="button" aria-haspopup="true" aria-expanded="false">Units <span class="caret"></span></a>
            <ul class="dropdown-menu">
              <li><a href="#">Action</a>
              </li>
              <li><a href="#">Another action</a>
              </li>
              <li><a href="#">Something else here</a>
              </li>
              <li role="separator" class="divider"></li>
              <li><a href="#">Separated link</a>
              </li>
              <li role="separator" class="divider"></li>
              <li><a href="#">One more separated link</a>
              </li>
            </ul>
          </li>
          <li><a href="#">Clients</a>
          </li>
          <li><a href="#contact-me">Contact Me</a>
          </li>
        </ul>
      </div>
      <!-- /.navbar-collapse -->
    </div>
    <!-- /.container-fluid -->
  </nav>


  <section class="section1">
    <div class="hero"></div>


    <a href="#section2"><i class="fa fa-angle-down" style="font-size:100px;"></i></a>

  </section>
  <section class="section2" id="section2">


    <a href="#contact-me"> <i class="fa fa-angle-down" style="font-size:100px;"></i></a>

  </section>
  <section id="contact-me" class="contact_section">

  </section>
  <script src="https://code.jquery.com/jquery-3.1.1.js" integrity="sha256-16cdPddA6VdVInumRGo6IbivbERE8p7CQR3HzTBuELA=" crossorigin="anonymous"></script>
  <script src="https://maxcdn.bootstrapcdn.com/bootstrap/3.3.7/js/bootstrap.min.js"></script>

</body>

<footer></footer>

</html>

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