How do you define a CSS variable?

Defining a CSS variable involves using the --variable-name syntax, which is typically placed within a :root selector or any specific element selector. The :root selector is a special selector in CSS that targets the highest level of the document tree, making it a suitable place for defining variables that should be available throughout the entire document.

The syntax for CSS variables is structured as follows:

:root {

--main-color: blue;

}

In this example, --main-color is a custom property (or CSS variable) that can be reused throughout other CSS rules. By defining CSS variables this way, they can enable better maintainability and allow for dynamic styling across different elements of a webpage. They also help in creating themes or adapting styles based on certain conditions without the need to rewrite extensive CSS.

While the other choices provided might involve CSS or other programming features, they do not accurately depict the standard method for defining CSS variables.