如何为导航栏文本的下拉菜单文本和中心下拉菜单文本重复下划线CSS？

Question

问题1

当我将鼠标悬停在框底部的下拉菜单中的导航栏文本上方时，将显示下划线。 但是，我希望导航栏下拉菜单文本发生此过程。 当用户将鼠标悬停在下拉菜单文本上方而不是下划线位于文本底部时，它位于下拉菜单框的底部。 我怎样才能做到这一点？

问题2

如何使导航栏下拉菜单文本在网页中依次显示？

这是我所有带有html和CSS的codepen 。

下方的HTML

<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

添加display: block; position: relative; display: block; position: relative; 到下拉菜单中的li和a 。 该边界基于绝对定位的元素，并且相对于最接近的非静态定位的祖先定位了绝对定位的元素。 并且使它们都处于阻塞状态将确保它们位于自己的行上，并且已应用到父级的text-align: center将起作用。

 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; } 

 <!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>