wp-duckbehaviorjournal/assets/js/lightbox.js

jQuery(document).ready(function() {
    const $ = jQuery;
    $('div.wp-caption a:first-child').click(function(event) {
        event.preventDefault();
        var imgSrc = $(this).attr('href');
        $('#lightbox-img').attr('src', imgSrc);
        $('#lightbox').fadeIn();
    });

    $('.lightbox-close').click(function() {
        $('#lightbox').fadeOut();
    });

    $(document).click(function(event) {
        if ($(event.target).is('#lightbox')) {
            $('#lightbox').fadeOut();
        }
    });
});