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I want to make a button with an icon using Glyphicons in Bootstrap, but the icon is not displayed.
I'm copying the class name from Bootstrap's official website, so I don't think it's a typo.

<! doctype html>
<html>
<head>
  <!-Required meta tags->
  <meta charset = "utf-8">
  <meta name = "viewport" content = "width = device-width, initial-scale = 1, shrink-to-fit = no">
  <!-Bootstrap CSS->
  <link rel = "stylesheet" href = "https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/css/bootstrap.min.css" integrity = "sha384-JcKb8q3iqJ61gNV9KGb8thSsNjpSL0n8PARn9HuZOnIxN0hoP + VmmDGMN5t9" crossJ0
  <title></title>
</head>
<body>
    
    <button>
      <span aria-hidden = "true"></span>Download
    </button>
    
  <!-Optional JavaScript->
  <!-JQuery first, then Popper.js, then Bootstrap JS->
  <script src = "https://code.jquery.com/jquery-3.5.1.slim.min.js" integrity = "sha384-DfXdz2htPH0lsSSs5nCTpuj/zy4C + OGpamoFVy38MVBnE + IbbVYUew + OrCXaRkfj" cross origin = "anonymous"></script>
  <script src = "https://cdn.jsdelivr.net/npm/[email protected]/dist/umd/popper.min.js" integrity = "sha384-9/reFTGAW83EW2RDu2S0VKaIzap3H66lZH81PoYlFhbGU + 6BZp6G7niu735Sk7lN" cross "></script>
  <script src = "https://stackpath.bootstrapcdn.com/bootstrap/4.5.2/js/bootstrap.min.js" integrity = "sha384-B4gt1jrGC7Jh4AgTPSdUtOBvfO8shuf57BaghqFfPlYxofvL8/KUEfYiJOMMV + rV" crossorigin
</body>
</html>


When previewing, it looks like the following and the icon is not displayed.
It seems that there is no particular error when verifying the element.

(Previewed on Google chrome.)

Please let me know if anyone knows the cause of this! !!