How to Add Page Slug in Body Class of your WordPress Themes - https://www.wpbeginner.com/wp-themes/how-to-add-page-slug-in-body-class-of-your-wordpress-themes/

slug-to-body-class.php

<?php
/*
Plugin Name: Slug to Body Class
Version: 0.1
Plugin URI: http://www.wpbeginner.com/wp-themes/how-to-add-page-slug-in-body-class-of-your-wordpress-themes/
Description: Add Page/Post Slug to Body Class
Author: Syed Balkhi
Author URI: https://plus.google.com/101623299936375408403/
*/

// From: http://www.wpbeginner.com/wp-themes/how-to-add-page-slug-in-body-class-of-your-wordpress-themes/
add_filter( 'body_class', 'add_slug_body_class' );
function add_slug_body_class($classes) {
    global $post;
    if ( isset( $post ) ) {
        $classes[] = $post->post_type . '-' . $post->post_name;
    }
    
    return $classes;
}