Why does ajax move the div to the right?

Question

AJAX

css:

.pagemain {
            margin: 500px;
            width: 50%;
            margin-top: 70px;
        }

ajax:

function mode() {
            $.ajax({
                url: "/app",
                success: function(data) {
                    $('#page-wrapper').html(data);
                }
            });
        };
        setInterval(mode, 1000);

html:

<div id = "page-wrapper" class="page-wrapper">
     <img src="img.jpg"/>
</div>

with ajax:


without ajax:

Answer 1

Run through the resulting house and understand what the mistake is.