Two php questions

Hi there,
I’ve decided to bite the bullet & learn PHP! To do this I’m following a set of tutorials to create new page useing ACF and I’m getting a blank screen (code below)!
Firstly: In the tutorial there is a line:
add_theme_support( 'genesis-structural-wraps', array( 'header', 'footer-widgets', 'footer', 'nav', 'subnav', ) );
I haven’t got clue what this is or how to point it at Harmonic – Help please!

Secondly: When I try to look at the page I get a blank screen, F12 also shows no style sheets – again, help please!!
Many thanks

Code (in it’s own file):

<?php

/**
 * Template Name: HomePageNewPaul1
 */

add_action('full_width_content','do_full_width_content');

add_filter('body_class', 'add_full_width_body_class' );
function add_full_width_body_class($classes){
    
     $classes[] = 'full-width-template';
 
 return $classes;
 
}

function do_full_width_content() {

?>

<main>
    
<?php
    
 // check if the flexible content field has rows of data 
 
if( have_rows('flexible_content') ):
 
  // loop through the rows of data
    while ( have_rows('flexible_content') ) : the_row(); 
 
  // check current row layout 
         if( get_row_layout() == 'hero' ):?>   
             
              <section>
                 <div class='hero' style="background-image:url(<?php the_sub_field('flexible_image')?>)"></div>
                
                 
             </section>
   
    
    
   endif;

endwhile;

else:

    //do something

    endif;

?>

</main>

<?php

 
 
 get_header();

do_action('full_width_content');

 get_footer();

Added to style.css:

    #full_width_template .site_inner{
    max-width:100%;
    padding: 0;
}
/* Section 1 -- Hero Section */ 
.hero {
 background-size: cover;
 background-position: center;
}
 
.cta_container {
 text-align: center;
 vertical-align: middle;
 background-color: rgba(0, 0, 0, 0.52);
 background: rgba(0, 0, 0, 0.52);
 color:rgba(0, 0, 0, 0.52);
}
 
.cta_content {
 padding: 100px 10px;
 color: white;
}

The page I need help with: [log in to see the link]