redwerks

This plugin allows posts and pages to have individual custom backgrounds. A full-body background that shows up on the post page itself can be specified. As well as background that just covers the content area and shows up on all places the post is visible.

Post Backgrounds

Allows posts and pages to have individual custom backgrounds. Both as body backgrounds and as content backgrounds.

Ryan Novotny

Add the particles.js JavaScript library to add cool particle effects to any WordPress page ( demo: <a href="https://particlebackground.com/" rel="nofollow ugc">https://particlebackground.com/</a> ).
Uses shortcode or easy options for adding to the front page or blog page of WordPress.
Fully customize the particles using your own JSON or the built in color & density settings
Leave a comment in the support forum for any suggestions or bugs.
<h4>Features</h4>
Add particle background to home or blog pages with one click 
Add particle background to any page using shortcodes 
Customize the background color and dot color 
Add any HTML just like a WordPress post to display on top of the particle background (optional)

Particle Background WP

Particle Backgrounds WP lets you easily add cool particle-style backgrounds to any page.

Post Backgrounds vs Particle Background WP