CSS, Cascading Style Sheets, is the coding language that defines what websites (such as this one!) look like in terms of fonts, colors, sizes, positioning and so on.
Certian colors in CSS have been given their own names, so that they can be referred to in code by that name instead of the somewhat harder-to-read Hex or RGB formats.
This CSS Colors study mug presents a mosaic canvas of all unique named colors, together with their Hex code and RGB values. A must-have companion on every web developers desk!