<!DOCTYPE html>
<html lang="en">
<head>
  <meta charset="UTF-8">
  <meta name="viewport" content="width=device-width, initial-scale=1.0">
  <meta http-equiv="X-UA-Compatible" content="ie=edge">
  <link rel="stylesheet" href="https://use.fontawesome.com/releases/v5.8.2/css/all.css" integrity="sha384-oS3vJWv+0UjzBfQzYUhtDYW+Pj2yciDJxpsK1OYPAYjqT085Qq/1cq5FLXAZQ7Ay" crossorigin="anonymous">
  <title>search animation</title>
</head>
<body>
  <div class="search-box">
  <input class="search-input" type="text" placeholder="Digita aqui">
    <a href="#" class="search-btn">
      <i class="fas fa-search"></i>
    </a>
  </div>  
</body>
</html>
* {
  padding: 0;
  margin: 0;
}

body {
  background-color: #e84118;
}

.search {
  &-box {
    position: absolute;
    top: 50%;
    left: 50%;
    transform: translate(-50%, -50%);
    background: #2f3640;
    height: 40px;
    border-radius: 40px;
    padding: 10px;
  }
  
  &-btn {
    color: #e84118;
    float: right;
    width: 40px;
    height: 40px;
    border-radius: 50%;
    background: #2f3640;
    display: flex;
    justify-content: center;
    align-items: center;
    transition: 0.4s;
    cursor: pointer;
  }
  
  &-input {
    border: none;
    background: none;
    outline: none;
    float: left;
    color: white;
    font-size: 16px;
    transition: all .6s;
    line-height: 40px;
    width: 0px;
  }
  
}

.search-box:hover > .search-input {
  width: 400px;
  padding: 0 6px;
}

.search-box:hover > .search-btn {
  background: white;
  color: black;
}
View Compiled

External CSS

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External JavaScript

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