Template CSS for AMP

I trying to use this instruction: https://ampforwp.com/tutorials/article/override-blacklist-sanitizer/#comment-4716
But I think in the last code mistake:

add_action('amp_post_template_css','new_css_for_form',999);
function new_css_for_form(){ ?>
	.amp-wp-content form>div {
	display:none;
} 

At least it ‘s extra or incomplete {
But I ‘m not a programmer.
Can someone help ?