Css underline animation when hover AND when active-CodePudding

I am trying to make a simple navigation menu consisting of buttons with an animating underline. Im using reactjs lib

I can't figure out how to have the underline visible immediately if the button element is active.

.btn {
  position: relative;
  text-transform: uppercase;
  color: whitesmoke;
  font-size: 1.4rem;
  cursor: pointer;
}

.btn:hover {
  color: whitesmoke;
  text-decoration: none;
}

.btn:before {
  content: "";
  position: absolute;
  width: 100%;
  height: 0.105rem;
  left: 0;
  bottom: 0;
  visibility: hidden;
  background-color: whitesmoke;
  transform: scaleX(0);
  transition: all 0.3s ease-in-out 0s;
}

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

button.active .btn:before {
  visibility: visible;
  transform: scaleX(1);
}

<a href="/">
  <button id="home" className="btn active">
              Home
            </button>
</a>
</div>
<div className="col-4 col-sm-2">
  <a href="/blog">
    <button id="blog" className="btn">
              Blog
            </button>
  </a>

CodePudding user response：

<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta http-equiv="X-UA-Compatible" content="IE=edge">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <link rel="stylesheet" href="./style.css">
  <title>Document</title>
</head>
<body>
  <a href="/">
  <button id="home" >
              Home
            </button>
</a>
</div>
<div className="col-4 col-sm-2">
  <a href="/blog">
    <button id="blog" >
              Blog
            </button>
  </a>
</body>
</html>

.btn {
    position: relative;
    text-transform: uppercase;
    color: whitesmoke;
    font-size: 1.4rem;
    cursor: pointer;
    border: none;
    outline: none;
    background-color: #332e2e77;
    display: inline-block;
    margin-bottom: 2rem;
}

a {
    display: inline-block;
}

.btn:hover {
    color: whitesmoke;
    text-decoration: none;
}

.btn::before {
    content: '';
    position: absolute;
    width: 0%;
    height: 0.105rem;
    left: 0;
    bottom: 0;
    visibility: hidden;
    background-color: rebeccapurple;
    transition: all 0.3s ease-in-out;
    -webkit-transition: all 0.3s ease-in-out;
    -moz-transition: all 0.3s ease-in-out;
    -ms-transition: all 0.3s ease-in-out;
    -o-transition: all 0.3s ease-in-out;
}

.btn:hover::before {
    width: 100%;
    visibility: visible;
}

.btn.active {
    position: relative;
}

.btn.active::after {
    content: '';
    position: absolute;
    width: 100%;
    height: 0.105rem;
    left: 0;
    bottom: 0;
    background-color: rebeccapurple;
    transition: all 0.3s ease-in-out;
    -webkit-transition: all 0.3s ease-in-out;
    -moz-transition: all 0.3s ease-in-out;
    -ms-transition: all 0.3s ease-in-out;
    -o-transition: all 0.3s ease-in-out;
}

try hovering now. className -> class as stated in comments I've used width 0% -> width 100%; and underline animates properly.

.btn:hover::before

-> you select pseudo selectors that way