How to use different CSS for different .ejs files in Node.js/Express?

For example, in layout.ejs, we specify a global css "css/bootstrap.min.css" which affects all pages.

<!DOCTYPE html>
<html lang="en">
  <head>
    <title>Example</title>
    <link href="css/bootstrap.min.css" rel="stylesheet">
  </head>
  <body>
    <%- body %>
  </body>
</html>

And we have a signup.ejs as follows

<div class="container">
  <form method="post" action="/signup">
    <p>
      Username: <input type="text" name="username" /><br />
      Email: <input type="text" name="email" /><br />
      Password: <input type="password" name="password" /><br />
      <input class="button" type="submit" value="Sign up" />
    </p>
  </form>
</div>

How do we add "css/signup.css" specifically for the signup.ejs page?