How to Correct WordPress Sidebar Below Content Layout.
This is a common error, happens when your website’s sidebar is no longer next to the main content where it should be but instead moves below it.
Solution for Sidebar Below Content
This is a common problem and the reason for this is that you have too many div tags open or closed. Have you copied and texted some text. Go to text view in the editor and delete <div> or </div> until the sidebar returns to its proper position.
<div>or </div> are used as a division or a section in an HTML document
With one too many or too few, elements close or open in the wrong place, this can cause your sidebar to push down your page.
A WordPress Quick Tip.
Tick the box this tells WordPress to correct invalidly(incorrect) nested XHTML automatically under Settings >> Writing Settings.
If your wordpress detects an incorrectly nested div, it will add a closing div to correct it automatically.