WordPress styles and scripts including

enqueue.php

<?php
function my_plugin_add_scripts(){
  wp_enqueue_style('my-plugin-style', plugins_url().'/my-plugin/css/style.css');
  wp_enqueue_script('my-plugin-script', plugins_url().'/my-plugin/js/main.js');
}
add_action('wp_enqueue_scripts', 'my_plugin_add_scripts');