Answers for "where to add custom css in wordpress"

how to add css file in wordpress

wp_enqueue_style( 'style', get_stylesheet_uri() );

how to add custom html and css in wordpress

/* I have just tried running your code on a fresh WordPress install with 
the Neve theme installed. Its all working correctly, except do not use .
container as a class for the flex box, instead use something like .
container-flex.
.container is already assigned to some HTML in the Neve theme.
I was unable to gain access to the site you want to use this on. But if you 
just need to add this onto a page, use the Custom HTML block, paste in your 
HTML code and save the page. */

<span> <div class ="container-flex">
	<div class ="box-zeeland" > Zeeland   </div>
  <div class ="box-normandie" > Normandy </div>
  <div class ="box-roffa" > Rotterdam </div>
  <div class ="box-Valencia" > Valencia  </div>
  <div class ="box-Adam" > Amsterdam </div>
  <div class ="overlay" > </div>
	</div> 
</span>

/* Then click on Customize > Additional CSS, and paste your CSS code in there 
and click Publish. Then your code should work as intended.*/

add stylesheet wordpress

function wpdocs_theme_name_scripts() {
    wp_enqueue_style( 'style-name', get_stylesheet_uri() );
    wp_enqueue_script( 'script-name', get_template_directory_uri() . '/js/example.js', array(), '1.0.0', true );
}
add_action( 'wp_enqueue_scripts', 'wpdocs_theme_name_scripts' );