How to create a child theme for RokoPhoto

All you need to do is create one folder, and stylesheet and functions file. And make sure that you have FTP access, before you continue reading this documentation. 
Log into your website using your favorite FTP client, such as FileZilla, and navigate to wp-content/themes/ directory. This is the directory where all your themes are living a happy life.
Now, you need to create a new folder for your child theme. You can name it anything. In this example, we will be creating a child theme of RokoPhoto , so we will name it RokoPhoto-child.

Once you have created your folder, you need to create a style.css file inside that folder. Your stylesheet will consist some vital information inside it, so paste the following in it using your favorite text editor:

   /*
   Theme Name: RokoPhoto Child
   Theme URI: https://www.themeisle.com/ 
   Description: This is a custom child theme I have created.
   Author: Chuck Norris Author
   URI: https://www.themeisle.com/ 
   Template: RokoPhoto
   Version: 0.1 
   */

Now, we need to load the stylesheet of the parent theme. Create a file named functions.php in the child theme folder, edit it, and paste the following:

<?php
function rokophoto_child_styles() {

    $rokophoto_bootstrap = 'rokophoto_bootstrap';

    wp_enqueue_style( 'rokophoto_parent', get_template_directory_uri() . '/style.css',
        array( $rokophoto_bootstrap  )
    );
}
add_action( 'wp_enqueue_scripts', 'rokophoto_child_styles' );
if ( get_stylesheet() !== get_template() ) {
    add_filter( 'pre_update_option_theme_mods_' . get_stylesheet(), function ( $value, $old_value ) {
         update_option( 'theme_mods_' . get_template(), $value );
         return $old_value; // prevent update to child theme mods
    }, 10, 2 );
    add_filter( 'pre_option_theme_mods_' . get_stylesheet(), function ( $default ) {
        return get_option( 'theme_mods_' . get_template(), $default );
    } );
}
?>

That's all. You just to save your progress and that's it.