Not a flat you live inside, like in the UK – but a flat piece of cardboard.
Source Appleshadow
Derived from an image that was uploaded to Pixabay by mdmelo.
Source Firkin
Brushed aluminum, in a bright gray version. Lovely 2X as well.
Source Andre Schouten
A bit strange this one, but nice at the same time.
Source Diogo Silva
There are many carbon patterns, but this one is tiny.
Source Designova
Based on an image that was uploaded to Pixabay by devanath
Source Firkin
A monochrome pattern from a tile that can be had by selecting the rectangle in Inkscaope and using shift+alt+i
Source Firkin
Like the name suggests, this background image consists of a pattern of dark bricks. It may be an option for you, if you are looking for something that looks like a brick wall for use as a background on web pages. It's not a masterpiece, but looks pretty nice when is tiled.
Source V. Hartikainen
Formed by distorting an image on Pixabay that was uploaded by gustavorezende. To get the tile this is based on, select the rectangle in Inkscape and use shift+alt+i.
Source Firkin
From a drawing in 'Artists and Arabs', Henry Blackburn, 1868.
Source Firkin
Number 2 in a series of 5 beautiful patterns. Can be found in colors on the submitter’s website.
Source Janos Koos
This metal background pattern resembles a metal plate with rivets. Solid rivets on a metal plate.
Source V. Hartikainen
The image depicts a seamless pattern of pine tree leaves.
Source Yamachem
Remixed from a JPG that was uploaded to Pixabay by susanlu4esm
Source Firkin
A seamless pattern from a tile made from a jpg on Pixabay. To get the tile select the rectangle in Inkscape and use shift-alt-i.
Source Firkin
Background Wall, Art Abstract, Blue Well & CC0 texture.
Source Ractapopulous
Dark and hard, just the way we like it. Embossed triangles makes a nice pattern.
Source Ivan Ginev
Not even 1kb, but very stylish. Gray thin lines.
Source Struck Axiom
Prismatic Geometric Tessellation Pattern 2 No Background
Source GDJ
To get the tile this is based on, select the rectangle in Inkscape and use shift-alt-i.
Source Firkin