eolant

/**
 * Adjust contact form 7 radios and checkboxes to match bootstrap 4 custom radio structure.
 */
add_filter('wpcf7_form_elements', function ($content) {
    $content = preg_replace('/<label><input type="(checkbox|radio)" name="(.*?)" value="(.*?)" \/><span class="wpcf7-list-item-label">/i', '<label class="custom-control custom-\1"><input type="\1" name="\2" value="\3" class="custom-control-input"><span class="wpcf7-list-item-label custom-control-label">', $content);

    return $content;
});

ayamflow

// Add on element with overflow
-webkit-mask-image: -webkit-radial-gradient(white, black);