Bootstrap 5 Ya

Ejemplo
Vista Previa

<!doctype html>
<html>
<head>
  <title>Prueba de Bootstrap 5</title> 
  <meta charset="utf-8">
  <meta name="viewport" content="width=device-width, initial-scale=1, shrink-to-fit=no">
  <link href="https://cdn.jsdelivr.net/npm/bootstrap@5.0.0/dist/css/bootstrap.min.css" rel="stylesheet" integrity="sha384-wEmeIV1mKuiNpC+IOBjI7aAzPcEZeedi5yW5f2yOq55WWLwNGmvvx4Um1vskeMj0" crossorigin="anonymous">
</head>
<body>

<form>
      <div class="mb-3 form-floating">        
        <input type="text" class="form-control" id="nombre" name="nombre" placeholder="usuario">        
        <label for="nombre" class="form-label">Usuario:</label>
      </div>
      <div class="mb-3 form-floating">
        <input type="password" class="form-control" id="clave" name="clave" placeholder="clave">
        <label for="clave" class="form-label">Clave:</label>        
      </div>
      <button type="submit" class="btn btn-primary">Confirmar</button>
    </form>

</div> 
</body>
</html>