This background image has seamless texture that resembles a surface of gray stone.
Source V. Hartikainen
A dark pattern made out of 3×3 circles and a 1px shadow. This works well as a carbon texture or background.
Source Atle Mo
Prismatic Curved Diamond Pattern 6 No Background
Source GDJ
This pattern comes in orange, and it looks as if it is "made of glass".
Source V. Hartikainen
Derived from an image that was uploaded to Pixabay by Darkmoon1968
Source Firkin
A seamless chequerboard pattern formed from a tile that can be had in Inkscape by selecting the rectangle and using shift+alt+i. Alternative colour scheme.
Source Firkin
Fix and cc0 to get the tile this is based on.
Source SliverKnight
Medium gray fabric pattern with 45-degree lines going across.
Source Atle Mo
Background Wall, Art Abstract, Blue Well & CC0 texture.
Source Ractapopulous
From a drawing in 'Art Embroidery', M.S. Lockwood and E. Glaister, 1878.
Source Firkin
This is a remix of "flower seamless pattern".I rotated the original image by 90 degrees.This is a seamless pattern of flowers.These horizontal wavy lines are one of Edo patterns which is called "tatewaku or tachiwaku or 立湧" that represents uprising steam or vapor.
Source Yamachem
Colorful Floral Background 3 No Black
Source GDJ
Inspired by a drawing in 'Poems', James Smith, 1881.
Source Firkin
Don’t look at this one too long if you’re high on something.
Source Luuk van Baars
Prismatic Geometric Tessellation Pattern 4 No Background
Source GDJ
With a name like this, it has to be hot. Diagonal lines in light shades.
Source Isaac
It looks like a polished stone surface to me. Download it for free, as always.
Source V. Hartikainen
This one resembles a black concrete wall when is tiled. It should look great, at least with dark website themes.
Source V. Hartikainen
An abstract texture of black metal pipes (seamless).
Source V. Hartikainen
Remixed from a drawing in 'Line and form', Walter Crane, 1914.
Source Firkin