The first image display a scrollbar, while the second one does not.
It all comes down to the .tabulator CSS class and specifically the border property.
How come only a 1px border impacts the scroll feature instead of affecting the entire content?
https://i.sstatic.net/ifeoj.jpg
Let's take a look at the HTML structure...
<!DOCTYPE html>
<html>
<head></head>
<body>
<div class="container">
<div class="navigation"></div>
<div id="content-full" class="tabulator"></div>
</div>
</body>
</html>