CSS Selectors

MUIT

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

We can divide CSS selectors into five categories:

Table of Contents

The CSS element Selector

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

Here, all <p> elements on the page will be center-aligned, with a red text color:

p {
  text-align: center;
  color: red;
}

Example 1

index.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS</title>

    <link rel="stylesheet" href="style.css">

</head>

<body>
    <p>Every paragraph will be affected by the style.</p>
    <p id="para1">Me too!</p>
    <p>And me!</p>

</body>

</html>

style.css

p {
    text-align: center;
    color: red;
}

Result View Example

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.

#para1 {
  text-align: center;
  color: red;
}

Example 2

index.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS ex2</title>

    <link rel="stylesheet" href="style.css">

</head>

<body>
    <p id="para1">Hello World!</p>
    <p>This paragraph is not affected by the style.</p>
</body>

</html>

style.css

#para1 {
    text-align: center;
    color: red;
}

Result View Example

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 3-1

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

index.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS ex3-1</title>

    <link rel="stylesheet" href="style.css">

</head>

<body>

    <h1 class="center">Red and center-aligned heading</h1>
    <p class="center">Red and center-aligned paragraph.</p>

</body>

</html>

style.css

.center {
    text-align: center;
    color: red;
}

Result View Example

Example 3-2

In this example only

elements with class="center" will be red and center-aligned:

index.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS ex3-2</title>

    <link rel="stylesheet" href="style.css">

</head>

<body>
    <h1 class="center">This heading will not be affected</h1>
    <p class="center">This paragraph will be red and center-aligned.</p>
</body>

</html>

style.css

p.center {
    text-align: center;
    color: red;
}

Result View Example

Example 3-3

In this example the

element will be styled according to class="center" and to class="large":

Note: A class name cannot start with a number!

index.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS</title>

    <link rel="stylesheet" href="style.css">

</head>

<body>

    <h1 class="center">This heading will not be affected</h1>
    <p class="center">This paragraph will be red and center-aligned.</p>
    <p class="center large">This paragraph will be red, center-aligned, and in a large font-size.</p>

</body>

</html>

style.css

p.center {
    text-align: center;
    color: red;
}

p.large {
    font-size: 300%;
}

Result View Example

The CSS Universal Selector

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

Example 4

index.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS ex4</title>

    <link rel="stylesheet" href="style.css">

</head>

<body>
    <h1>Hello world!</h1>

    <p>Every element on the page will be affected by the style.</p>
    <p id="para1">Me too!</p>
    <p>And me!</p>

</body>

</html>

style.css

* {
    text-align: center;
    color: blue;
}

Result View Example

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):

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

To group selectors, separate each selector with a comma.

h1, h2, p {
  text-align: center;
  color: red;
}

Example 5

index.html

<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>CSS</title>

    <link rel="stylesheet" href="style.css">

</head>

<body>

    <h1>Hello World!</h1>
    <h2>Smaller heading!</h2>
    <h3>No group</h3>
    <p>This is a paragraph.</p>

</body>

</html>

style.css

h1,
h2,
p {
    text-align: center;
    color: red;
}

Result View Example

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