Setting Up 404 Page Not Found in Blogger

Blogger has featured "404" page customization.
Just a fact:

The 404 or Not Found error message is a HTTP standard response code indicating that the client was able to communicate with the server, but the server could not find what was requested.
The web site hosting server will typically generate "404 - Not Found" web page, when users attempts to follow a broken or dead link, hence the 404 error is one of the most recognizable errors users can find on the web

To start this,  you need to upgrade your Blogger  to a new look.
Then, follow the instruction below:

 

Inside the black border is where you can add your custom 404-Not Found Page 

You can use this conditional tag to hide the widgets for your 404 page.

<b:if cond='data:blog.pageType == "error_page"'>
<style type="text/css">
PUT YOUR CSS CODE HERE
</style>
</b:if>

 or this code

<b:if cond='data:blog.url != &quot;YOUR BLOG URL/404.html&quot;'>
<style>
PUT YOUR CSS CODE HERE
</style>
</b:if>

I think it works the same. Take a look at my 404-Not Found Page 
You can put image

 <img src="LINK OF THE IMAGE"/>

or just a simple message/text on the page. Add the HTML CODE after the </b:if> tag or before <b:if cond='blahblah'>. Then Save it!


For further explanation visit this link.