<?php
// functions.php

add_shortcode( 'contentbox', 'mw_shortcode_contentbox' );

function mw_shortcode_contentbox( $attrs, $content = '' ) {
    $parsed_attrs = shortcode_atts( array(
        'align' => ''
    ), $attrs );
  
    return "<aside class='content-box " . $parsed_attrs['align'] . "'>" . $content . "</aside>";
}

?>