All about css selectors

CSS selectors

In CSS, selectors are used to target the HTML elements on our web pages that we want to style. There are a wide variety of CSS selectors available, allowing for fine-grained precision when selecting elements to style. In this article and its sub-articles we’ll run through the different types in great detail, seeing how they work.

Prerequisites:	Basic computer literacy, 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 how CSS selectors work in detail.

What is a selector?

A CSS selector is the first part of a CSS Rule. It is a pattern of elements and other terms that tell the browser which HTML elements should be selected to have the CSS property values inside the rule applied to them. The element or elements which are selected by the selector are referred to as the subject of the selector.

In other articles you may have met some different selectors, and learned that there are selectors that target the document in different ways — for example by selecting an element such as h1 , or a class such as .special .

In CSS, selectors are defined in the CSS Selectors specification; like any other part of CSS they need to have support in browsers for them to work. The majority of selectors that you will come across are defined in the Level 3 Selectors specification and Level 4 Selectors specification, which are both mature specifications, therefore you will find excellent browser support for these selectors.

Selector lists

If you have more than one thing which uses the same CSS then the individual selectors can be combined into a selector list so that the rule is applied to all of the individual selectors. For example, if I have the same CSS for an h1 and also a class of .special , I could write this as two separate rules.

h1  color: blue; > .special  color: blue; > 

I could also combine these into a selector list, by adding a comma between them.

White space is valid before or after the comma. You may also find the selectors more readable if each is on a new line.

In the live example below try combining the two selectors which have identical declarations. The visual display should be the same after combining them.

When you group selectors in this way, if any selector is syntactically invalid, the whole rule will be ignored.

In the following example, the invalid class selector rule will be ignored, whereas the h1 would still be styled.

h1  color: blue; > ..special  color: blue; > 

When combined however, neither the h1 nor the class will be styled as the entire rule is deemed invalid.

Types of selectors

There are a few different groupings of selectors, and knowing which type of selector you might need will help you to find the right tool for the job. In this article’s subarticles we will look at the different groups of selectors in more detail.

Type, class, and ID selectors

This group includes selectors that target an HTML element such as an .

It also includes selectors which target a class:

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CSS Selectors

A CSS selector selects the HTML element(s) you want to style.

CSS Selectors

CSS selectors are used to «find» (or select) the HTML elements you want to style.

We can divide CSS selectors into five categories:

• Simple selectors (select elements based on name, id, class)
• Combinator selectors (select elements based on a specific relationship between them)
• Pseudo-class selectors (select elements based on a certain state)
• Pseudo-elements selectors (select and style a part of an element)
• Attribute selectors (select elements based on an attribute or attribute value)

This page will explain the most basic CSS selectors.

The CSS element Selector

The element selector selects HTML elements based on the element name.

Example

Here, all

elements on the page will be center-aligned, with a red text color:

The CSS id Selector

The id selector uses the id attribute of an HTML element to select a specific element.

The id of an element is unique within a page, so the id selector is used to select one unique element!

To select an element with a specific id, write a hash (#) character, followed by the id of the element.

Example

The CSS rule below will be applied to the HTML element with

Note: An id name cannot start with a number!

The CSS class Selector

The class selector selects HTML elements with a specific class attribute.

To select elements with a specific class, write a period (.) character, followed by the class name.

Example

In this example all HTML elements with will be red and center-aligned:

You can also specify that only specific HTML elements should be affected by a class.

Example

In this example only

elements with will be red and center-aligned:

HTML elements can also refer to more than one class.

Example

In this example the

element will be styled according to and to

This paragraph refers to two classes.

Note: A class name cannot start with a number!

The CSS Universal Selector

The universal selector (*) selects all HTML elements on the page.

Example

The CSS rule below will affect every HTML element on the page:

The CSS Grouping Selector

The grouping selector selects all the HTML elements with the same style definitions.

Look at the following CSS code (the h1, h2, and p elements have the same style definitions):

h2 text-align: center;
color: red;
>

p text-align: center;
color: red;
>

It will be better to group the selectors, to minimize the code.

To group selectors, separate each selector with a comma.

Example

In this example we have grouped the selectors from the code above:

All CSS Simple Selectors

Selector	Example	Example description
#id	#firstname	Selects the element with >
.class	.intro	Selects all elements with >
element.class	p.intro	Selects only elements with >
*	*	Selects all elements
element	p	Selects all elements
element,element.	div, p	Selects all elements and all elements

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