How to remove CSS?

I’m trying to remove WPEM’s CSS file. I’ve tried the typical functions.php method…

function deregister_wpem_css() {
	wp_deregister_style('wpem_css');
}
add_action('wp_print_styles', 'deregister_wpem_css');

and

function deregister_wpem_css() {
	wp_deregister_style('wpem_css-css');
}
add_action('wp_print_styles', 'deregister_wpem_css');

What am I doing wrong? Is there some other way to remove the CSS?

(For added bonus info: I’m removing the CSS because I want to style it myself!)

http://ww.wp.xz.cn/plugins/wp-employment/