Add Divi Meta Box to custom post type

gistfile1.php

// Add Divi Meta Box to custom post type
add_action( 'add_meta_boxes', 'divi_add_post_meta_box' );
function divi_add_post_meta_box() {
    add_meta_box( 'et_settings_meta_box', esc_html__( 'Divi Post Settings', 'Divi' ), 'et_single_settings_meta_box', 'custom_post_type_slug', 'side', 'high' );
}

if ( ! function_exists( 'et_single_settings_meta_box' ) ) :
function et_single_settings_meta_box( $post ) {
	$post_id = get_the_ID();

	wp_nonce_field( basename( __FILE__ ), 'et_settings_nonce' );

	$page_layout = get_post_meta( $post_id, '_et_pb_page_layout', true );

	$side_nav = get_post_meta( $post_id, '_et_pb_side_nav', true );

	$project_nav = get_post_meta( $post_id, '_et_pb_project_nav', true );

	$post_hide_nav = get_post_meta( $post_id, '_et_pb_post_hide_nav', true );
	$post_hide_nav = $post_hide_nav && 'off' === $post_hide_nav ? 'default' : $post_hide_nav;

	$show_title = get_post_meta( $post_id, '_et_pb_show_title', true );

	$page_layouts = array(
		'et_right_sidebar'   => esc_html__( 'Right Sidebar', 'Divi' ),
		'et_left_sidebar'    => esc_html__( 'Left Sidebar', 'Divi' ),
		'et_full_width_page' => esc_html__( 'Full Width', 'Divi' ),
	);

	$layouts = array(
		'light' => esc_html__( 'Light', 'Divi' ),
		'dark'  => esc_html__( 'Dark', 'Divi' ),
	);
	$post_bg_color  = ( $bg_color = get_post_meta( $post_id, '_et_post_bg_color', true ) ) && '' !== $bg_color
		? $bg_color
		: '#ffffff';
	$post_use_bg_color = get_post_meta( $post_id, '_et_post_use_bg_color', true )
		? true
		: false;
	$post_bg_layout = ( $layout = get_post_meta( $post_id, '_et_post_bg_layout', true ) ) && '' !== $layout
		? $layout
		: 'light'; ?>

	<p class="et_pb_page_settings et_pb_page_layout_settings">
		<label for="et_pb_page_layout" style="display: block; font-weight: bold; margin-bottom: 5px;"><?php esc_html_e( 'Page Layout', 'Divi' ); ?>: </label>

		<select id="et_pb_page_layout" name="et_pb_page_layout">
		<?php
		foreach ( $page_layouts as $layout_value => $layout_name ) {
			printf( '<option value="%2$s"%3$s>%1$s</option>',
				esc_html( $layout_name ),
				esc_attr( $layout_value ),
				selected( $layout_value, $page_layout, false )
			);
		} ?>
		</select>
	</p>
	<p class="et_pb_page_settings et_pb_side_nav_settings" style="display: none;">
		<label for="et_pb_side_nav" style="display: block; font-weight: bold; margin-bottom: 5px;"><?php esc_html_e( 'Dot Navigation', 'Divi' ); ?>: </label>

		<select id="et_pb_side_nav" name="et_pb_side_nav">
			<option value="off" <?php selected( 'off', $side_nav ); ?>><?php esc_html_e( 'Off', 'Divi' ); ?></option>
			<option value="on" <?php selected( 'on', $side_nav ); ?>><?php esc_html_e( 'On', 'Divi' ); ?></option>
		</select>
	</p>
	<p class="et_pb_page_settings">
		<label for="et_pb_post_hide_nav" style="display: block; font-weight: bold; margin-bottom: 5px;"><?php esc_html_e( 'Hide Nav Before Scroll', 'Divi' ); ?>: </label>

		<select id="et_pb_post_hide_nav" name="et_pb_post_hide_nav">
			<option value="default" <?php selected( 'default', $post_hide_nav ); ?>><?php esc_html_e( 'Default', 'Divi' ); ?></option>
			<option value="no" <?php selected( 'no', $post_hide_nav ); ?>><?php esc_html_e( 'Off', 'Divi' ); ?></option>
			<option value="on" <?php selected( 'on', $post_hide_nav ); ?>><?php esc_html_e( 'On', 'Divi' ); ?></option>
		</select>
	</p>

<?php if ( 'custom_post_type_slug' === $post->post_type) : ?>
<p class="et_pb_page_settings et_pb_single_title" style="display: none;">
<label for="et_single_title" style="display: block; font-weight: bold; margin-bottom: 5px;"><?php esc_html_e( 'Post Title', 'Divi' ); ?>: </label>

<select id="et_single_title" name="et_single_title">
<option value="on" <?php selected( 'on', $show_title ); ?>><?php esc_html_e( 'Show', 'Divi' ); ?></option>
<option value="off" <?php selected( 'off', $show_title ); ?>><?php esc_html_e( 'Hide', 'Divi' ); ?></option>
</select>
</p>
<?php endif; ?>


<?php if ( 'post' === $post->post_type ) : ?>
	<p class="et_pb_page_settings et_pb_single_title" style="display: none;">
		<label for="et_single_title" style="display: block; font-weight: bold; margin-bottom: 5px;"><?php esc_html_e( 'Post Title', 'Divi' ); ?>: </label>

		<select id="et_single_title" name="et_single_title">
			<option value="on" <?php selected( 'on', $show_title ); ?>><?php esc_html_e( 'Show', 'Divi' ); ?></option>
			<option value="off" <?php selected( 'off', $show_title ); ?>><?php esc_html_e( 'Hide', 'Divi' ); ?></option>
		</select>
	</p>

	<p class="et_divi_quote_settings et_divi_audio_settings et_divi_link_settings et_divi_format_setting et_pb_page_settings">
		<label for="et_post_use_bg_color" style="display: block; font-weight: bold; margin-bottom: 5px;"><?php esc_html_e( 'Use Background Color', 'Divi' ); ?></label>
		<input name="et_post_use_bg_color" type="checkbox" id="et_post_use_bg_color" <?php checked( $post_use_bg_color ); ?> />
	</p>

	<p class="et_post_bg_color_setting et_divi_format_setting et_pb_page_settings">
		<input id="et_post_bg_color" name="et_post_bg_color" class="color-picker-hex" type="text" maxlength="7" placeholder="<?php esc_attr_e( 'Hex Value', 'Divi' ); ?>" value="<?php echo esc_attr( $post_bg_color ); ?>" data-default-color="#ffffff" />
	</p>

	<p class="et_divi_quote_settings et_divi_audio_settings et_divi_link_settings et_divi_format_setting">
		<label for="et_post_bg_layout" style="font-weight: bold; margin-bottom: 5px;"><?php esc_html_e( 'Text Color', 'Divi' ); ?>: </label>
		<select id="et_post_bg_layout" name="et_post_bg_layout">
	<?php
		foreach ( $layouts as $layout_name => $layout_title )
			printf( '<option value="%s"%s>%s</option>',
				esc_attr( $layout_name ),
				selected( $layout_name, $post_bg_layout, false ),
				esc_html( $layout_title )
			);
	?>
		</select>
	</p>
<?php endif;

if ( 'project' === $post->post_type ) : ?>
	<p class="et_pb_page_settings et_pb_project_nav" style="display: none;">
		<label for="et_project_nav" style="display: block; font-weight: bold; margin-bottom: 5px;"><?php esc_html_e( 'Project Navigation', 'Divi' ); ?>: </label>

		<select id="et_project_nav" name="et_project_nav">
			<option value="off" <?php selected( 'off', $project_nav ); ?>><?php esc_html_e( 'Hide', 'Divi' ); ?></option>
			<option value="on" <?php selected( 'on', $project_nav ); ?>><?php esc_html_e( 'Show', 'Divi' ); ?></option>
		</select>
	</p>
<?php endif;
}
endif;