SOLUTION The solution way actually very simple. I found that it was really hard to find a good resource for the answer so I am answering here.

The style.css was missing: template: theme in the commented header i.e.

/*
 Theme Name:   samirTheme
 Theme URI:    http://example.com/twenty-fifteen-child/
 Description:  Twenty Fifteen Child Theme
 Author:       John Doe
 Author URI:   http://example.com
 Template:     twentyfifteen <--------------------------------------------
 Version:      1.0.0
 License:      GNU General Public License v2 or later
 License URI:  http://www.gnu.org/licenses/gpl-2.0.html
 Tags:         light, dark, two-columns, right-sidebar, responsive-layout, accessibility-ready
 Text Domain:  twenty-fifteen-child
*/

In order for WordPress to recognize the set of theme template files as a valid theme, the style.css file needs to be located in the root directory of your theme, not a subdirectory.

So main theme css file in root -> then enqueue a 2nd style sheet that has all the styles in it - if you want it to be in /css/

Example header of css:

/*
Theme Name: Twenty Seventeen
Theme URI: https://wordpress.org/themes/twentyseventeen/
Author: the WordPress team
Author URI: https://wordpress.org/
Description: Twenty Seventeen brings your site to life with immersive featured images and subtle animations. With a focus on business sites, it features multiple sections on the front page as well as widgets, navigation and social menus, a logo, and more. Personalize its asymmetrical grid with a custom color scheme and showcase your multimedia content with post formats. Our default theme for 2017 works great in many languages, for any abilities, and on any device.
Version: 1.0
License: GNU General Public License v2 or later
License URI: http://www.gnu.org/licenses/gpl-2.0.html
Text Domain: twentyseventeen
Tags: one-column, two-columns, right-sidebar, flexible-header, accessibility-ready, custom-colors, custom-header, custom-menu, custom-logo, editor-style, featured-images, footer-widgets, post-formats, rtl-language-support, sticky-post, theme-options, threaded-comments, translation-ready
This theme, like WordPress, is licensed under the GPL.
Use it to make something cool, have fun, and share what you've learned with others.
*/

For more info read this: https://developer.wordpress.org/themes/basics/main-stylesheet-style-css/

Same happened to me. I have all the necessary files (as two files only required index and style) one thing I have noticed if you have a folder for your style.css file you will get the error message as above.

So I cross-checked and even moved the and deleted the index file from the main folder.

If I delete index.php file from main folder, and place it inside the css folder it works.

I do not know why it happened. But it seems me it need an index file inside the style folder or style.css files to be placed in the main folder.