Hey, I just realized I haven't posted my list of websites for creative backgrounds here on dev.to yet - so here it is:
A list of easy customizable SVG backgrounds.
A huge collection of SVG pattern backgrounds by Steve Schoger.
A cool css library for background patterns, which can be easily applied to all elements.
A generator for low poly triangle patterns.
A large collection of CSS patterns, which can be filtered and colorized.
A bunch of nice backgrounds using the HTML5 Canvas API.
Repeatable SVG background patterns by Steve Schoger.
A web component for drawing patterns with CSS.
A cool generator for unique, royalty-free, repeatable SVG patterns by John Bartlet.
A compiled list of beautiful patterns by different designers.
A generator for SVG wave patterns.
A huge list of more than 500 subtle background patterns and textures.
A pretty space animation out of triangles using canvas.
A cool generator, which also has a small list of backgrounds created with it.
Create interactive backgrounds on this website.
Animated WebGL backgrounds with the possibility to customize.
A website, which combines the most popular gradient collections.
A generator for beautiful SVG patterns.
A collection of shapes created using WebGL.
A smoothly animated wave with pure CSS.
A site to create beautiful animated gradients for use on your website.
A configurable lightning simulation using canvas or SVG polygons.
A collection of pure css animated backgrounds with the possibility to customize.
Did I miss anything? Let me know in the comments :)