How to format an underline for a navigation bar using CSS

问题

I figured out how to make an underline under a part of my navigation bar when I am hovering over the word. I am trying to make it in the same format for when I am on that page so that the underline stays there. I can't figure this out. Would love some help. Thanks :)

*{
    margin:0;
    padding:0;
    border:0;
}


.topnav {
    background-color: purple;
    overflow: hidden;
  }
  
  .topnav a {
    float: left;
    color: #f2f2f2;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    font-size: 17px;
    position: relative;
  }

  .topnav a:before {
    content: "";
    position: absolute;
    width: 84%;
    height: 2px;
    bottom: 3px;
    left: 8%;
    background-color: white;
    visibility: hidden;
    transform: scaleX(0);
    transition: all 0.3s ease-in-out 0s;
  }

 .topnav a:hover:before {
    visibility: visible;
    transform: scaleX(1);
  }

<!DOCTYPE html>
<html lang="en">
<link rel="stylesheet" href="style.css">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>
    Change
  </title>
</head>

<body>
  <div class="topnav">
    <a class="active" href="index.html">Home</a>
    <a href="#news">DontUse</a>
    <a href="#contact">DontUse</a>
    <a href="about.html">About</a>
  </div>
  <p>
    This is the home page
  </p>
</body>

</html>

回答1:

Here you go, using jquery. Also made a new active-menu class .topnav a.active-menu:before

$("a").click(function(){
   $("a.active-menu").removeClass("active-menu");
   $(this).addClass("active-menu");
});

*{
    margin:0;
    padding:0;
    border:0;
}


.topnav {
    background-color: purple;
    overflow: hidden;
  }
  
  .topnav a {
    float: left;
    color: #f2f2f2;
    text-align: center;
    padding: 14px 16px;
    text-decoration: none;
    font-size: 17px;
    position: relative;
  }

  .topnav a:before {
    content: "";
    position: absolute;
    width: 84%;
    height: 2px;
    bottom: 3px;
    left: 8%;
    background-color: white;
    visibility: hidden;
    transform: scaleX(0);
    transition: all 0.3s ease-in-out 0s;
  }

 .topnav a:hover:before {
    visibility: visible;
    transform: scaleX(1);
  }
.topnav a.active-menu:before {
    content: "";
    position: absolute;
    width: 84%;
    height: 2px;
    bottom: 3px;
    left: 8%;
    background-color: white;
    visibility: visible;
    transform: scaleX(1);
    transition: all 0.3s ease-in-out 0s; 
    }

<script src="https://cdnjs.cloudflare.com/ajax/libs/jquery/3.3.1/jquery.min.js"></script>
<!DOCTYPE html>
<html lang="en">
<link rel="stylesheet" href="style.css">

<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <title>
    Change
  </title>
</head>

<body>
  <div class="topnav" id="topnav">
    <a class="active-menu" href="index.html">Home</a>
    <a class="link" href="#news">DontUse</a>
    <a class="link" href="#contact">DontUse</a>
    <a class="link" href="about.html">About</a>
  </div>
  <p>
    This is the home page
  </p>
</body>

</html>

来源：https://stackoverflow.com/questions/61786026/how-to-format-an-underline-for-a-navigation-bar-using-css

标签

html

css

format

underline