How to Change Background Image of Any Blogger Templates

As we  know the blogger templates are very simple you can change its background image by simply going to Template > Customize > Background
But for some unique template either you have create your own or download from third party site which design templates.
if you upload any third party site template you can't change background by doing above method.

To Change Background Image
1. From your blogger Dashboard > Template > Edit HTML > Proceed
Make sure to click on the Expand widget box (highly recommended)
2. Using Ctrl + F, Find-
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 body{
background:url(http://www.example.com/image.png)repeat top center;

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3. Replace existing url from your image url

or

To simply find exiting url by 
go to home page of your blog  
Right Click mouse button > View Background Image  
by copy-paste image url from address bar to Find box using ctrl+f  
to find that url in Template > Edit HTML  
Replace it with your image url

 

Image Position (in this case your whole screen). You can use add one of the following variables: 

 

top center 

top right

top left   

bottom left

bottom center 

bottom right

* center left
* center center
* center right

To specify how the image repeats itself:

add "no-repeat"  (No repeat)  (without quote)add "repeat"   (Repeats Y and X also known as tiled) 
add "repeat-x"  (Repeats Horizontal)
add "repeat-y"  (Repeats Vertical) 

To specify whether the image moves when your scroll or whether it stays in place.
add "fixed"  (to fixed background image)
add "scroll"  (Scrolls with screen)

 After you are done the code may look like the one below:
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body{
background: url(http://www.yourimageurl.com/image.jpg) no-repeat top center fixed;
or
body{
background: url(http://www.yourimageurl.com/image.jpg) no-repeat top center;
background-attachment: fixed;
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To Change the Background Color of Your Custom Blogger Template

1. From your blogger Dashboard > Template > Edit HTML > Proceed
Using Ctrl + F

Find the line with :
body{ 
background-color: #

2. Replace the existing hex color code with the value of your chosen hex color

3. background-color: #change existing hex color code to your chosen color;
List of web safe hex colors. For example insert the following code to change the background color to: 
Denim Blue 
background-color: #336699;
Black 

background-color: #000000;
White 

background-color: #ffffff;

NOTE:  Use the Preview button to see the effect of each color & background image before you save it.
You can try are Wallpapers as background images.
That's all, i hope this post helps you plz feel free to ask any query.