Primary Button for my plugin button?

Hello, I was practicing with custom WordPress plugins and I tried the following code:

<?php
/*
 Plugin Name: Ontdubbelaar
 Description: Het ontdubbelen van dubbelingen
 Version: 1.0
 License: GPL
 Author: Anon
 Author URI: anon.test.nl
 */

function uploadFile() {

	?>
	<div class="wrap">
	<h2> Test </h2>
	<form action="" method="post" >
  		<input type="submit" name="test" value="submit"	class="button-primary" />
    </form>
	</div>
	<?php
};
add_shortcode('upload','uploadFile');
?>

When I call the shortcode [upload] the button appears aswell as the h2 but the css class “button-primary” does not apply on the button. What am I missing, do I have to include the path of css in my plugin?