I just want to put the CSS's content inside tag <style amp-custom>
This is my action inside function
function amp_template_add_styles() {
$stylesheets = get_template_directory_uri() . '/material/public/app.min.css';
echo file_get_contents( $stylesheets );
}
add_action( 'amp_template_css', 'amp_template_add_styles', 99 );
And i call the function insider tag <head>
<style amp-custom>
<?php do_action( 'amp_template_css', 'amp_template_add_styles'); ?>
</style>
And this is the error when i implement in this way
There are anyone knows about this, please help me, thanks