Add class to functions.php custom code to call font awesome icon

Question

I have inherited a website that has custom code in the functions.php file to create a custom Tab in Woocommerce products. This will eventually become obsolete as I update the site but for now I need to insert a font awesome Icon before the Tab Title Text

Below is the code that appears in the functions.php, how do I add a Font Awesome Icon to appear before the Title 'TECHNICAL DOCUMENTS'. The font awesome class is "fas fa-book"

    add_filter( 'woocommerce_product_tabs', 'add_product_specs_tab' );
function add_product_specs_tab( $tabs ) {
    $tabs['product_specs'] = [
        'title'     => __( 'TECHNICAL DOCUMENTS', 'woocommerce' ),
        'priority'  => 50,
        'callback'  => 'add_product_specs_tab_content'
    ];

    return $tabs;

}
function add_product_specs_tab_content() {
    global $post;
    $pdf = get_field( 'pdf', $post->ID );
    
    if ( ! $pdf ) {
        echo "<h3>Sorry!! No Spec for This Product</h3>";
    } else {
        echo '<div id="product-download-specs-btn">';
        echo '<h3>Download the Product Spec below</h3>';
        echo sprintf( '<a href="%s">Download</a>', $pdf );
        echo '</div>';
        if ( ! is_user_logged_in() ) {
            echo '<div id="product-download-specs-form" data-pdf="'.$pdf.'">';
            echo apply_shortcodes('[contact-form-7 id="33372396" title="Product Spec"]');
            echo '</div>';
        }
    }
}

The desired outcome would be as follows:

Answer 1

There's no need to add another class. The code you're using already creates separate classes and ID. You could do this with just css:

Inspect your site with console, but your div label should be technical_documents so your code would be:

#tab-title-technical_documents a::before {
  content: "\f02d";
  font-family: 'Font Awesome 6';
  font-weight: 900;
}

You didn't mention which version of font-awesome you're using, so you may have to change the font-family to match your version. (Again, you could check your console and see which version the other two tabs are using.)