Drupal has many odd things hard-wired into it. The one I want to get into today is how, in Drupal 7, the <body> element has classes attached to it that sometimes just don’t make sense.
Let’s say you enable a theme, and your <body> element looks like this:
<body class="html front logged-in no-sidebars page-node" >
This happens for me when I have created a new Aurora based sub-theme. The only most of the classes are fine, but the
no-sidebars class is the odd duck.