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I have 404 error message when open portfolio items.

It’s because of permalinks and how WP manage slugs. Try this. Add
flush_rewrite_rules();
to bra_theme_functions.php (Appearance -> Editor) in function create_post_type(), so it should look like this
function create_post_type() {
    register_post_type( 'portfolio_item',
        array(
            'labels' => array(
                'name' => __( 'Portfolio Items' ),
                'singular_name' => __( 'Portfolio Item' ),
                'add_item' => __('New Portfolio Item'),
                'add_new_item' => __('Add New Portfolio Item'),
                'edit_item' => __('Edit Portfolio Item')
            ),
            'public' => true,
            'has_archive' => true,
            //'rewrite' => false,

            'rewrite' => array('slug' => 'portfolio'),
            'menu_position' => 5,
            'show_ui' => true,
            'supports' => array('author', 'title', 'editor', 'thumbnail', 'excerpt', 'custom-fields', 'revisions', 'post-formats', 'comments')

        )
    );
flush_rewrite_rules();
}
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