Stimulate

var new = document.createElement('div');
new.innerHTML = xhr.responseText;
var old = document.getElementById('mydiv');
var parent = old.parentNode;
parent.insertBefore(old, new);
old.remove();

https://jsfiddle.net/qn20x7mL/3/

Землякам привет

/wp-content/themes/storefront/style.css

33 строка, удалите "width: 21.7391304348%;"

$var = 123456789;
echo number_format($var, 0, ' ', ' ');