dynamic name of the style for wp_enqueue_style

this syntax doesn’t seem right to me.

First of all what is ABS_URL? If it’s a constant that you’ve defined earlier, then there is an ' missing before /includes/box.css'. The code should look like this:

$name="mystyle";
wp_enqueue_style( $name .'-style', ABS_URL . '/includes/box.css', false );

It works as it should, the output is: <link rel="stylesheet" id='mystyle-style-css' href="https://wordpress.stackexchange.com/questions/284788/whatever-there-is-in-ABS_URL-constant" type="text/css" media="all" />

Also, make sure if you need to define this constant at all – if you want to load stylesheet from your theme’s folder or its subfolders, use get_stylesheet_directory_uri() function:

$name="mystyle";
wp_enqueue_style( $name .'-style', esc_url( get_stylesheet_directory_uri() ) . '/includes/box.css' , false );