How to add meta description field to pages (not posts)?

Hello.

I’m using the following code (from Tom I think, or maybe another member of the GeneratePress team) to display the meta description field on posts, which works great; however, I want to do the same for pages as I have a custom homepage to which I want to add meta description without the need of course of any SEO plugin.

How can I change it to perform the same for both posts and pages?

1- Here is the code I’m using to create a custom field for Meta Description to display below posts in the editor:

function add_seo_custom_fields() {
add_meta_box(
'seo_custom_fields', // Unique ID
'SEO', // Box title
'render_seo_custom_fields', // Content callback, must be of type callable
'post', // Post type
'normal', // Context
'high' // Priority
);
}
add_action( 'add_meta_boxes', 'add_seo_custom_fields' );

function render_seo_custom_fields( $post ) {
$meta_description = get_post_meta( $post->ID, 'meta_description', true );
wp_nonce_field( basename( FILE ), 'seo_custom_fields_nonce' );
?>


Meta Description:
<?php echo esc_textarea( $meta_description ); ?>

<?php
}

function save_seo_custom_fields( $post_id ) {
$is_autosave = wp_is_post_autosave( $post_id );
$is_revision = wp_is_post_revision( $post_id );
$is_valid_nonce = ( isset( $_POST[ 'seo_custom_fields_nonce' ] ) && wp_verify_nonce( $_POST[ 'seo_custom_fields_nonce' ], basename( FILE ) ) ) ? 'true' : 'false';

if ( $is_autosave || $is_revision || !$is_valid_nonce ) {
return;
}

if ( isset( $_POST[ 'meta_description' ] ) ) {
update_post_meta( $post_id, 'meta_description', sanitize_text_field( $_POST[ 'meta_description' ] ) );
}
}
add_action( 'save_post', 'save_seo_custom_fields' );

2- Here is the code I’m using to allow adding Meta Description content to its field:

add_action( 'wp_head', function() {
    if ( is_singular() ) {
        $post_id = get_the_ID();

        // Set meta title to post title if custom meta title is not set
        $meta_title = get_post_meta( $post_id, 'meta_title', true );
        if ( ! $meta_title ) {
            $meta_title = get_the_title( $post_id );
        }

        // Set meta description to first 160 characters of post content, stripped of HTML tags, if custom meta description is not set
        $meta_desc = get_post_meta( $post_id, 'meta_description', true );
        if ( ! $meta_desc ) {
            $post_content = get_post_field( 'post_content', $post_id );
            $meta_desc = mb_substr( wp_strip_all_tags( $post_content ), 0, 160 );
        }

        // Replace newline characters with spaces
        $meta_desc = str_replace( "\n", " ", $meta_desc );

        // Replace multiple spaces with a single space
        $meta_desc = preg_replace( '/\s+/', ' ', $meta_desc );

        // Output meta title and meta description
        if ( $meta_title ) {
            printf( '<meta name="title" content="%s"/>', $meta_title );
            echo "\n";  // Add a line break
        }

        if ( $meta_desc ) {
            printf( '<meta name="description" content="%s"/>', $meta_desc );
			echo "\n";  // Add a line break
        }
    }
} );

I guess probably that I would need to add ‘page’ as a post type in function add_seo_custom_fields(), but I’m not sure for the rest; I’m afraid to break the code as I’m not good in PHP.

Any help from you would be greatly appreciated.
Thank you.