Combinators
===========

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The final selectors we will look at are called combinators, because they combine other selectors in a way that gives them a useful relationship to each other and the location of content in the document.

|  |  |
| --- | --- |
| Prerequisites: | Basic software installed, basic knowledge of
 working with files, HTML basics (study
 Introduction to HTML), and an idea of how CSS works (study
 CSS first steps.)
  |
| Objective: | 
 To learn about the different combinator selectors that can be used in
 CSS.
  |

Descendant combinator
---------------------

The **descendant combinator** — typically represented by a single space (" ") character — combines two selectors such that elements matched by the second selector are selected if they have an ancestor (parent, parent's parent, parent's parent's parent, etc.) element matching the first selector. Selectors that utilize a descendant combinator are called *descendant selectors*.


```css
body article p
```


In the example below, we are matching only the `<p>` element which is inside an element with a class of `.box`.

Child combinator
----------------

The **child combinator** (`>`) is placed between two CSS selectors. It matches only those elements matched by the second selector that are the direct children of elements matched by the first. Descendant elements further down the hierarchy don't match. For example, to select only `<p>` elements that are direct children of `<article>` elements:


```css
article > p
```


In this next example, we have an unordered list, nested inside of which is an ordered list. The child combinator selects only those `<li>` elements which are direct children of a `<ul>`, and styles them with a top border.

If you remove the `>` that designates this as a child combinator, you end up with a descendant selector and all `<li>` elements will get a red border.

Next-sibling combinator
-----------------------

The **next-sibling combinator** (`+`) is placed between two CSS selectors. It matches only those elements matched by the second selector that are the next sibling element of the first selector. For example, to select all `<img>` elements that are immediately preceded by a `<p>` element:


```css
p + img
```


A common use case is to do something with a paragraph that follows a heading, as in the example below. In that example, we are looking for any paragraph which shares a parent element with an `<h1>`, and immediately follows that `<h1>`.

If you insert some other element such as a `<h2>` in between the `<h1>` and the `<p>`, you will find that the paragraph is no longer matched by the selector and so does not get the background and foreground color applied when the element is adjacent.

Subsequent-sibling combinator
-----------------------------

If you want to select siblings of an element even if they are not directly adjacent, then you can use the **subsequent-sibling combinator** (`~`). To select all `<img>` elements that come *anywhere* after `<p>` elements, we'd do this:


```css
p ~ img
```


In the example below we are selecting all `<p>` elements that come after the `<h1>`, and even though there is a `<div>` in the document as well, the `<p>` that comes after it is selected.

Creating complex selectors with nesting
---------------------------------------

The CSS nesting module allows you to write nested rules that use combinators to create complex selectors.


```css
p {
  ~ img {
  }
}
/\* This is parsed by the browser as \*/
p ~ img {
}
```


The `&` nesting selector can also be used to create complex selectors.


```css
p {
  & img {
  }
}
/\* This is parsed by the browser as \*/
p img {
}
```


**Note:** In the example above, the `&` nesting selector is not required, but adding it helps to explicitly show that CSS nesting is being used.

Using combinators
-----------------

You can combine any of the selectors that we discovered in previous lessons with combinators in order to pick out part of your document. For example, to select list items with a class of "a" which are direct children of a `<ul>`, try the following:


```css
ul > li[class="a"] {
}
```


Take care, however, when creating big lists of selectors that select very specific parts of your document. It will be hard to reuse the CSS rules since you have made the selector very specific to the location of that element in the markup.

It is often better to create a simple class and apply that to the element in question. That said, your knowledge of combinators will be very useful if you need to style something in your document and are unable to access the HTML, perhaps due to it being generated by a CMS.

Test your skills!
-----------------

You've reached the end of this article, but can you remember the most important information? You can find some further tests to verify that you've retained this information before you move on — see Test your skills: Selectors.

Summary
-------

This is the last section in our lessons on selectors. Next, we'll move on to another important part of CSS — the cascade, specificity, and inheritance.

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