If you are programer first thing you learned is about what variable is. It is value that can be changed but you can refer to it to get it’s value as many time you want. In CSS however in 2017…
CSS -posts about Cascading Style Sheets
CSS is stylesheet language used to describe presentation of HTML document and how elements should be rendered on media. For example, fonts, sizes, colours, margins, lines, height, width, background images, advanced positions and many other things.
It is primary design to separate HTML markup structure and how that structure should look like. This way markup could be shared, and presentation can vary reducing code duplication, complexety and making maintenance of them web page easier. Before it, all presentation attributes were contained in the HTML making it more complex. Currently there are three versions. Latest version CSS3, brings new features like rounded corners, box shadow, advanced selectors, gradients, box sizing, border images, media queries, multiple backgrounds and more. In this series of articles some latest features will be covered that are already there like flexbox and custom properties, and some that are yet to come.