Add Css Functions.php II

<?php 

function load_custom_css_and_js_files(){

    //This would get primary theme style.css    
    //wp_enqueue_style('custom_main_styles', get_stylesheet_uri());

    //Fetch Custom css hosted and cdn files. Notice how to import cdn
    wp_enqueue_style('font-awesome', '//maxcdn.bootstrapcdn.com/font-awesome/4.7.0/css/font-awesome.min.css');
    wp_enqueue_style('custom_main_styles', get_theme_file_uri('/build/style-index.css'));
    wp_enqueue_style('custom_extra_styles', get_theme_file_uri('/build/index.css'));

}

add_action('wp_enqueue_scripts', 'load_custom_css_and_js_files');