Returns the first element within the document…
Returns a list of the elements within the document…
IE in the first one, you’re operating on a single element, which does have a style
property. The second one is a list of elements, so you need to loop over that list applying the style:
var els = document.querySelectorAll("div#tabs" + tabId + "> div.page");
for (var x = 0; x < els.length; x++)
els[x].style.display = 'none';