<?php

add_shortcode('clearfix', 'clearfix_shortcode');

function clearfix_shortcode($args = [])    {
    $args_lc = array_map('strtolower', (array)$args);
    if (array_search('left', $args_lc) !== false) {
        $direction = 'left';
    }
    else if (array_search('right', $args_lc) !== false) {
        $direction = 'right';
    }
    else {
        $direction = 'both';
    }
    return '<div style="display:block;visibility:hidden;height:0;clear:' . $direction . ';"></div>';
}