nth-child

Calculate the nth-child equation for CSS selectors.

For example, if you wanted to have a selector for every third child element
(i.e. 1, 4, 7), you would use the selector nth-child(3n + 1). To calculate
this we can take the first two numbers, 1 and 4, and pair them with 0 and 1,
respectively. We treat each pair as an (x, y) coordinate pair where the
desired children numbers are the y coordinates (i.e. (0, 1) and (1, 4)). We
use these two coordinate pairs to calculate the linear equation that represents
the nth-child selector.

Install

$ npm install -g nth-child

Usage

$ nth-child n1 n2

Examples

#### Target every child starting with the second child

$ nth-child 2 3
n + 2

#### Target every third child

$ nth-child 1 4
3n + 1

#### Target the first two children

$ nth-child 2 1
-n + 2