CSS Selectors

CSS selectors are the foundation of web styling, allowing developers precise control over how styles are applied to HTML elements. From the Universal Selector for universal styling to more specific choices like Element Type, Id, and Class Selectors, each provides a targeted way to apply styles. Advanced techniques such as Descendant, Child, Adjacent Sibling, and General Sibling Selectors offer nuanced control, while Grouping Selectors streamline efficiency by consolidating styling rules. Mastering these CSS selectors is key to creating visually appealing, responsive, and well-organized websites.

A CSS selector is a pattern used to match components on a web page, and the associated style rules of the selector are applied to elements that match the pattern.

Selectors play a crucial role in CSS as they enable you to style specific components of your website in various ways.

CSS offers different types of selectors, let's examine them closely:

The universal selector (*) matches every element on the page. It is often used to remove default margins and paddings for testing purposes.

<style>
* {
    margin: 1;
    padding: 5;
}
</style>

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The * selector's style rules will be applied to all elements in the document.

Note: In a production setting, it is not suggested to use the universal selector (*) too frequently since it matches every element on a web page, putting undue strain on browsers. Instead, use the element type or class selector.

Element type selectors match all instances of a specific element type in the document.

<style>
h1 {
    color: purple;
}
p {
    color: green;
}
</style>

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The "p" selector will apply style rules to every <p> element in the document, regardless of its position in the document tree.

id selectors are used to style a single unique element.

They are denoted by the "#" symbol followed by the id value.

<style>    
#error {
    color:purple;
}
</style>

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The style rule with the id selector "#error" will apply to the element with the id property set to "error".

Class selectors target elements with a specific class attribute.

They are indicated by the "." symbol followed by the class value.

<style>    
.blue{
    color:skyblue;
}
</style>

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For instance, the style rules with the class selector ".blue" will be applied to all elements with the class attribute set to "blue".

<style>    
p.blue {
    color:red;
}
</style>

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Only those whose text is rendered in blue by the style rule inside the selection p.blue are rendered in blue by the style rule inside the selector p.blue. It has no effect on other paragraphs because the class property is set to blue.

Descendant selectors are used to select elements that are descendants of another element.

<style>
h1 em {
	color: orange;
}
ul.menu {
    padding: 5;
    list-style: none;
}
ul.menu li{
    display: inline;
}
ul.menu li a {
	margin: 15px;
	text-decoration: none;
}
</style>

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The selector "ul.menu li a" will only apply style rules to <a> elements that are within a <ul> element with the class ".menu".

Child selectors select elements that are direct children of another element. They are denoted by the ">" symbol.

<style>
ul > li {
	list-style: circle;
}
ul > li ol {
	list-style: none;
}
</style>

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To pick sibling items, utilise the nearby sibling selectors (i.e. elements at the same level). This selector has the following syntax: E1 + E2, where E2 is the selector's target.

In the following example, the selector h4 + p will only pick the <p> elements if both the <h4> and <p> elements have the same parent in the document tree and the <h4> element is immediately before the <p> element. That is, the accompanying style constraints will only apply to the paragraphs that follow each h4heading. Let's have a look at how this selection works in practise :

<style>
h1 + p {
	color: green;
	font-size: 20px;
}
ul.task + p {
	color: purple;
	text-indent: 35px;
}
</style>

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The neighbouring sibling selection (E1 + E2) is similar to the normal sibling selector, although it is less rigorous. Two simple selections are separated by< the tilde (~) character in a generic sibling selector. It may be represented as E1 E2, where E2 is the selector's target.

In the example below, the selector h1 ~ p will pick all the <p> elements that come before the <h1> element, as long as they all have the same parent in the document tree.

<style>
h1 ~ p {
	color: green;
	font-size: 20px;
}
ul.task ~ p {
	color: purple;
	text-indent: 20px;
}
</style>

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Attribute selectors, pseudo-classes, and pseudo-elements are examples of more advanced selectors. In the next chapters, we'll go through these selectors in depth.

A style sheet's selectors frequently have the same style rule declarations. To reduce the amount of code in your style sheet, arrange them into a comma-separated list. It also keeps you from having to repeat the same style guidelines over and again. Let's have a look at some examples:

<style>
h1 {
	font-size: 30px;
	font-weight: normal;
}
h2 {
	font-size: 25px;
	font-weight: normal;
}
h3 {
	font-size: 20px;
	font-weight: normal;
}
</style>

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Because the selectors h1, h2, and h3 all have the same style rule font-weight: normal;, they may be grouped in a comma-separated list like this:

<style>
h1, h2, h3 {
	font-weight: normal;
}
h1 {
	font-size: 30px;
}
h2 {
	font-size: 25px;
}
h3 {
	font-size: 20px;
}
</style>

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What are CSS selectors?

CSS selectors are patterns used to select and target HTML elements in a document for styling and manipulation. They allow you to apply specific styles to certain elements without affecting others.

What is the purpose of CSS selectors?

CSS selectors serve the purpose of identifying and targeting specific HTML elements within a webpage, enabling you to apply styles, layout changes, and interactivity to those elements selectively.

What are the different types of CSS selectors?

There are several types of CSS selectors:

• Universal Selector (*): Selects all elements in the document.
• Type Selector: Selects elements based on their HTML tag name (e.g., div, p, h1).
• Class Selector (.classname): Selects elements with a specific class attribute value.
• ID Selector (#idname): Selects an element with a specific ID attribute value.
• Descendant Selector (ancestor descendant): Selects elements that are descendants of another element.
• Child Selector (parent > child): Selects elements that are a direct child of another element.
• Adjacent Sibling Selector (element + sibling): Selects an element that is immediately preceded by a specific sibling element.
• General Sibling Selector (element ~ sibling): Selects sibling elements that share the same parent as the target element.

How does the class selector differ from the ID selector?

The class selector (.classname) is used to target multiple elements that share the same class attribute value, allowing you to apply the same styles to those elements. The ID selector (#idname), on the other hand, targets a single unique element with a specific ID attribute value, typically used for individual element styling or JavaScript manipulation. IDs should be unique within a page, while classes can be applied to multiple elements.

How can you select elements with multiple classes?

To select elements with multiple classes, you can combine class selectors without any space between them. For example: .class1.class2 will select elements that have both class1 and class2 applied to them.

Explain the difference between the descendant selector and the child selector?

The descendant selector (ancestor descendant) selects all elements that are descendants of the specified ancestor element, regardless of how many levels deep they are nested. The child selector (parent > child), on the other hand, selects only the immediate child elements of the specified parent element, ignoring elements nested deeper.

When would you use the adjacent sibling selector?

The adjacent sibling selector (element + sibling) is used to select an element that directly follows another specific element. This can be useful when you want to apply styles to an element that appears immediately after a certain element in the HTML structure.

What is the purpose of the pseudo-classes in CSS selectors?

Pseudo-classes are used to define the special state of an element that cannot be targeted using traditional selectors. For example, :hover is a pseudo-class that targets an element when a user hovers over it. Pseudo-classes are often used to add interactivity to elements or style specific states.

How can you select the first and last element of a certain type using CSS?

You can use the :first-of-type and :last-of-type pseudo-classes to select the first and last element of a certain type within their parent element. For example, p:first-of-type will select the first paragraph element within its parent.

What is the purpose of the :not() pseudo-class?

The :not() pseudo-class is used to select elements that do not match a specific selector. It allows you to exclude certain elements from a selection. For instance, p:not(.special) would select all paragraph elements except those with the class "special".

What is the difference between attribute selectors and pseudo-classes?

Attribute selectors target elements based on their attributes' values, allowing you to style elements that have specific attribute values. Pseudo-classes, on the other hand, target elements based on their state or position within the document. While both provide additional ways to select elements, attribute selectors focus on attributes, and pseudo-classes focus on states or positions.

How can you select all links that have been visited by the user?

You can use the :visited pseudo-class to select all links that have been visited by the user. For example, a:visited would select all visited anchor elements and allow you to apply specific styles to them.

What is the purpose of the :nth-child() pseudo-class?

The :nth-child() pseudo-class allows you to select elements based on their position within a parent element. It takes an argument in the form of an+b, where n represents the position of the element, and a and b are integers. This can be useful for styling alternating rows or specific patterns of elements.

How can you select only the input elements that are required within a form?

You can use the attribute selector to target input elements with the required attribute set to true. For example, input[required] will select all input elements that have the required attribute.

What is the :hover pseudo-class used for?

The :hover pseudo-class is used to target an element when a user hovers their cursor over it. It's commonly used to provide visual feedback or create interactive effects when users interact with elements like links, buttons, or images.

What is the purpose of the :before and :after pseudo-elements?

The :before and :after pseudo-elements allow you to insert content before or after the content of an element, respectively. They are often used in conjunction with the content property to add decorative or informative elements to the page without modifying the actual HTML structure.

What is the difference between the :nth-child() and :nth-of-type() pseudo-classes?

The :nth-child() pseudo-class selects elements based on their position among all children of the same parent, regardless of their element type. The :nth-of-type() pseudo-class, however, selects elements based on their position among siblings of the same element type. This means that :nth-of-type() will only consider elements with the same tag name.

What is the purpose of the attribute contains selector ([attribute*=value])?

The attribute contains selector allows you to select elements based on the partial value of an attribute. For instance, [href*="example"] would select all elements with an href attribute containing the word "example", regardless of its position within the attribute value.

How can you select only even or odd elements using CSS?

You can use the :nth-child() pseudo-class with the even and odd keywords to select even and odd elements, respectively. For example, tr:nth-child(even) will select all even rows within a table.

How can you select the last two elements in a container using CSS?

You can use the :nth-last-child() pseudo-class to select elements based on their position from the end. For example, p:nth-last-child(-n+2) will select the last two paragraph elements within their parent.

CSS selectors are the key to targeting specific elements on a web page and applying styles to them. By understanding and utilizing the wide range of CSS selectors, you gain precise control over which elements receive specific styles. Selectors allow you to target elements based on their type, class, ID, attributes, and even their position in the document tree.

The first set of CSS selectors includes the Universal Selector (*), which applies styles universally, and Element Type Selectors, allowing developers to style specific HTML elements based on their tag names. Id Selectors (#) come into play for uniquely identifying and styling a particular e lement, while Class Selectors (.) offer a way to style multiple elements with shared characteristics through the use of class attributes.

Moving on, descendant selectors, child selectors (>), adjacent sibling selectors (+), and general sibling selectors (~) provide more granular control over styling by targeting elements based on their relationships within the HTML structure. This hierarchical approach allows developers to create sophisticated layouts and designs. Finally, the flexibility of Grouping Selectors allows for efficient styling of multiple selectors within a single declaration block, streamlining the code and enhancing maintainability.

This gives you the ability to create highly customized and targeted styles for different parts of your web pages. With CSS selectors, you can efficiently and effectively style your website, making it visually appealing, user-friendly, and tailored to your design needs. So, embrace the power of CSS selectors and elevate your web design skills to new heights.