To hide the Blogger NavBar:

- Log in to blogger

- On your Dashboard, select Layout. This will take you to the Template tab. Click Edit HTML. Under the Edit Template section you will see you blog's HTML.

- paste the CSS definition in the top of the template code:

<b:skin><![CDATA[/*
-----------------------------------------------
Blogger Template Style
Name:     Rounders
Designer: Douglas Bowman
URL:      www.stopdesign.com
Date:     27 Feb 2004
Updated by: Blogger Team
----------------------------------------------- */

#navbar-iframe {
display: none !important;
}

/* Variable definitions
====================
<Variable name="mainBgColor" description="Main Background Color"
          type="color" default="#fff" value="#ffffff">
<Variable name="mainTextColor" description="Text Color" type="color"
          default="#333" value="#333333">
...

Remove the code to show it again.