how to add files in child theme in theme editor

1/*
2 Theme Name:   WPB Child Theme
3 Theme URI:    https://www.wpbeginner.com
4 Description:  A Twenty Thirteen child theme 
5 Author:       WPBeginner
6 Author URI:   https://www.wpbeginner.com
7 Template:     twentythirteen
8 Version:      1.0.0
9*/
10 
11@import url("../twentythirteen/style.css");
12 
13.site-title {
14padding: 30px 0 30px;
15}
16 
17.site-header .home-link {
18min-height: 0px;
19}
20 
21.navbar {
22background-color: #e8e5ce;
23}
24 
25.widget { 
26background-color: #e8e5ce;
27}
28.site-footer {
29background-color: #d8cdc1;
30} 
31.site-footer .sidebar-container { 
32background-color:#533F2A
33}
34

1add_action('after_setup_theme', function() {
2	$file = get_stylesheet_directory() . '/my-file.php';
3	if(!file_exists($file)) {
4		include_once ABSPATH . 'wp-admin/includes/file.php';
5		\WP_Filesystem();
6		global $wp_filesystem;
7		$wp_filesystem->put_contents($file, '', FS_CHMOD_FILE);
8	}
9});

1add_action('after_setup_theme', function() {
2	$file = get_stylesheet_directory() . '/my-file.php';
3	touch($file);
4});