theme-independent CSS/JS files

Use the following code to create a simple plugin. Create a directory tia inside plugins directory and save the code in a file tia.php then put it inside tia directory and finally activate from plugin page.

<?php
/**
 * Plugin Name: Theme Independent Assets
 * Author: Obi
 * Version: 0.0.7
 */

if ( ! defined( 'ABSPATH' ) ) {
    exit;
}

function tia_enqueue_scripts() {
    wp_enqueue_script( ... );
    wp_enqueue_style( ... );
}
add_action( 'wp_enqueue_scripts', 'tia_enqueue_scripts' );