autoloader.php

<?php
/**
 * WordPress Class Autoloader
 */
spl_autoload_register(
	function ( $classname ) {

		// Remove base.
		$classname = str_replace( 'BernskioldMedia\\WP\\PageSpecificCSS\\', '', $classname );

		// Regular
		$class     = str_replace( '\\', DIRECTORY_SEPARATOR, strtolower( $classname ) );
		$classpath = __DIR__ . DIRECTORY_SEPARATOR . 'src' . DIRECTORY_SEPARATOR . $class . '.php';

		// WordPress
		$parts   = explode( '\\', $classname );
		$class   = strtolower( array_pop( $parts ) );
		$class   = str_replace( '_', '-', $class );
		$folders = strtolower( implode( DIRECTORY_SEPARATOR, $parts ) );
		$folders = str_replace( '_', '-', $folders );
		$wppath  = __DIR__ . DIRECTORY_SEPARATOR . 'src' . DIRECTORY_SEPARATOR . $folders . DIRECTORY_SEPARATOR . $class . '.php';

		if ( file_exists( $classpath ) ) {
			  require_once $classpath;
		} elseif ( file_exists( $wppath ) ) {
			require_once $wppath;
		}

	}
);