A seamlessly repeating background pattern of wood. The image is procedurally generated, and, I think, it's turned out quite well.
Source V. Hartikainen
Sweet and subtle white plaster with hints of noise and grunge.
Source Phil Maurer
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
This pack of filters can help you adding a blocky overlay to objects. May come handy at drawing blocks of stone.
Source Lazur URH
Abstract Ellipses Background Grayscale
Source GDJ
Seamless pattern formed from a tile that can be extracted by selecting the rectangle in Inkscape and using shift-alt-i.
Source Firkin
Square design drawn in Paint.net and vectorized in Vector Magic.
Source Firkin
Zerro CC tillable texture of stones photographed and made by me. CC0
Source Sojan Janso
Light gray paper pattern with small traces of fiber and some dust.
Source Atle Mo
Pattern formed from simple shapes. Black version.
Source Firkin
An alternative colour scheme for the original background.
Source Firkin
To get the tile this is made up from select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
A free seamless background texture that looks like a brown stone wall.
Source V. Hartikainen
Remixed from a raster on Pixabay that was uploaded by ArtsyBee.
Source Firkin
This is so subtle I hope you can see it! Tweak at will.
Source Alexandre Naud
A light brushed aluminum pattern for your pleasure.
Source Tim Ward
Vertical lines with a bumpy, yet crisp, feel to it.
Source Raasa
You know, tiny and sharp. I’m sure you’ll find a use for it.
Source Atle Mo
From a drawing in 'The Quiver of Love', Walter Crane, 1876
Source Firkin
You know, tiny and sharp. I’m sure you’ll find a use for it.
Source Atle Mo
Looks like a technical drawing board: small squares forming a nice grid.
Source We Are Pixel8