What is nth-child?

, The `nth-child` selector provides developers with a more precise and flexible way to select and style elements. By properly using the `nth-child` selector, we can easily select and style various elements with specific positions, making our page design richer and more diverse.

In front-end development, a CSS selector is a syntax rule for selecting specific elements. Among CSS selectors, `nth-child` is a commonly used pseudo-class selector.

The `nth-child` selector allows you to select specific elements based on their position in the parent element, and filter out the required elements based on certain rules. It selects elements by using simple mathematical formulas, which allows developers to more precisely select, control and style elements in different positions.

The syntax of the `nth-child` selector is as follows:

:nth-child(an+b)

Where `a` and `b` are both integer values ​​and must be positive integers.

`a` is a period value, indicating how many elements every other, while `b` represents the starting position to be selected. Specifically, `an b` means that the position of the element in the parent element conforms to Only the rules of `an b` will be selected.

The following are some examples to help understand the application scenarios of the `nth-child` selector:

1. `:nth-child(odd)`: Select all elements in odd positions.

2. `:nth-child(even)`: Select all even-numbered elements.

3. `:nth-child(3n)`: Select the first of every 3 elements.

4. `:nth-child(3n 1)`: Select the first element of every 3 elements.

5. `:nth-child(2n 1)`: Select the first element of every 2 elements.

Let’s go through the following example to better understand how the `nth-child` selector works.

Suppose there is an HTML list (ul) containing 9 li elements, and we want to select some of them for style setting.

Element 1

Element 2

Element 3

Element 4

Element 5

Element 6

Element 7

Element 8

Element 9

Case 1: Select elements at odd positions (i.e. 1st, 3rd, 5th, 7th, 9th elements ):

li:nth-child(odd) {
background-color: yellow;
}

Case 2: Select the elements at even positions (i.e. the 2nd, 4th, 6th, and 8th elements):

li:nth-child(even) {
background-color: green;
}

Case 3: Select the first of every 3 elements elements (that is, the 1st, 4th, and 7th elements):

li:nth-child(3n+1) {
color: red;
}

Through these examples, we can see the power of the `nth-child` selector. It can select and style specific elements based on their position within parent elements. This provides designers and developers with more creative freedom and control possibilities.

However, it should be noted that CSS selectors may have compatibility differences in different browsers. Therefore, when using the `nth-child` selector, developers should test and adjust the compatibility of different browsers to ensure that the code written can work properly in different environments.

To sum up, the `nth-child` selector provides developers with a more precise and flexible way to select and style elements. By properly using the `nth-child` selector, we can easily select and style various elements with specific positions, making our page design richer and more diverse. .

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