In most of these effects the single source background-image url is repeated one or more times and blended with itself using CSS blend modes (multiply, overlay, screen, difference, etc.)
In some of these effects, the CSS filter property is used to further refine the output. Functions like grayscale(), brightness(), and contrast() can and should be tweaked to achieve a better result for images you use.
These effects should be used as a progressive enhancement. By default, the source image is displayed without any effects. When CSS @supports detects support for the required CSS properties and values for an individual effect, then the effect will be enabled. This amounts to a precise, native, and lightweight feature detection.
A complete CSS library of these effects can be downloaded unminified (12.8kb) or minified (8.7kb). Using gzip, the entire image effects library is less than 1300 bytes. github