/* Step 1: Create a new directory in your themes directory. Let's call it 'mytheme-child' */

/* Step 2: Create a style.css file in the new directory and add the following: */

/*
Theme Name:   My Child Theme
Template:     twentynineteen
Version:      1.0.0
*/

/* Step 3: Enqueue Parent and Child theme stylesheets. Add the following code in your functions.php file */

function my_theme_enqueue_styles() {

    $parent_style = 'parent-style';

    wp_enqueue_style( $parent_style, get_template_directory_uri() . '/style.css' );
    wp_enqueue_style( 'child-style',
        get_stylesheet_directory_uri() . '/style.css',
        array( $parent_style ),
        wp_get_theme()->get('Version')
    );
}
add_action( 'wp_enqueue_scripts', 'my_theme_enqueue_styles' );

/* Step 1: Create a PHP file in your child theme directory and name it 'custom_widget.php'

/* Step 2: In this file, define a class that extends the WP_Widget class. */

class My_Custom_Widget extends WP_Widget {

    /* Step 3: Define the four methods */

    // The construct function
    function __construct() {
        parent::__construct(
            // Base ID of your widget
            'my_custom_widget', 

            // Widget name will appear in UI
            __('My Custom Widget', 'my_custom_widget_domain'), 

            // Widget description
            array( 'description' => __( 'A Custom Widget', 'my_custom_widget_domain' ), ) 
        );
    }

    // Creating widget front-end
    public function widget( $args, $instance ) {
        $title = apply_filters( 'widget_title', $instance['title'] );

        // Before and after widget arguments are defined by themes
        echo $args['before_widget'];
        if ( ! empty( $title ) )
        echo $args['before_title'] . $title . $args['after_title'];

        // This is where you run the code and display the output
        echo __( 'Hello, World!', 'my_custom_widget_domain' );
        echo $args['after_widget'];
    }

    // Widget Backend
    public function form( $instance ) {
        if ( isset( $instance[ 'title' ] ) ) {
            $title = $instance[ 'title' ];
        }
        else {
            $title = __( 'New title', 'my_custom_widget_domain' );
        }
        // Widget admin form
        ?>
        <p>
        <label for="<?php echo $this->get_field_id( 'title' ); ?>"><?php _e( 'Title:' ); ?></label> 
        <input class="widefat" id="<?php echo $this->get_field_id( 'title' ); ?>" name="<?php echo $this->get_field_name( 'title' ); ?>" type="text" value="<?php echo esc_attr( $title ); ?>" />
        </p>
        <?php 
    }

    // Updating widget replacing old instances with new
    public function update( $new_instance, $old_instance ) {
        $instance = array();
        $instance['title'] = ( ! empty( $new_instance['title'] ) ) ? strip_tags( $new_instance['title'] ) : '';
        return $instance;
    }
} // Class my_custom_widget ends here

/* Step 4: Register your custom widget */

// Register and load the widget
function my_load_widget() {
    register_widget( 'my_custom_widget' );
}
add_action( 'widgets_init', 'my_load_widget' );