What Is CSS?
CSS (Cascading Style Sheets) is a language used to define the visual appearance and layout of web pages written in HTML or XML.
It allows developers to control various aspects of a page’s design—such as fonts, colors, background images, and overall structure—making it easy to tailor the look and feel to user preferences or design requirements. CSS is not limited to screen displays; it also supports styling for other media types, including printed pages and even screen readers used by visually impaired users.
Prerequisites
You should have a basic understanding of HTML before learning CSS.
Since CSS is used to style web pages written in HTML, it's important to at least know what HTML is before you start writing CSS.
Introduction to CSS
CSS, which stands for Cascading Style Sheets—a style sheet language that applies style rules in a cascading or hierarchical manner—is used to define the design and layout of web pages.
While HTML is used to define the structure and semantic meaning of a web page’s content, CSS specifies how that content is visually presented. In other words, CSS is the language used to control the style—commonly referred to as the “design”—of a web page.
Note:
Although CSS is primarily used to style the visual appearance of web pages in browsers, it can also specify how content is presented in other media—such as how pages appear when printed—and even control aspects of speech output for screen readers used by visually impaired users.
CSS is the language used to style HTML elements
CSS is a language used to style the visual presentation of web page content.
Web pages are built using HTML elements, and CSS is the language used to design those elements.
In other words, CSS styles the HTML elements that make up a web page.
Note:
In addition to HTML elements, browsers also display XML elements, which are structured similarly to HTML. CSS can be used to style XML as well. This topic will be covered later.
HTML is a markup language, but CSS is not a markup language, nor is it a programming language. CSS is a style sheet language used to select elements marked up in an HTML document and apply styles to them. It is the standard way to implement the styling of web pages.
While JavaScript can also be used to create visual effects and design elements, it relies on CSS to apply styles. In other words, JavaScript does not directly handle the styling of web pages on its own—it works alongside CSS to control presentation.
Let’s look at a CSS example
Suppose you want to style text on a web page to appear in red. The following is a simple example of how to apply that style to an HTML element using CSS.
p: Selects the<p>element to apply styles to it.color: red;: Sets the text color to red.
When you use CSS to select elements marked up in HTML and apply styles, the browser displays the web page with those styles applied.
The example above shows how to style the text color of an HTML <p> element using CSS.
With CSS, you can apply styles to various elements on a web page—not only text color but also background images, layouts, and more.
Key Features of CSS
CSS is a stylesheet language composed of code written to specify the design, layout, and style of web pages. A stylesheet language is one that defines the style and formatting of a document, and CSS specifically defines the style and formatting of HTML documents.
In addition to CSS, there are other stylesheet languages such as Sass, Less, and Stylus. These languages extend or simplify CSS, helping developers work more efficiently when styling web pages.
By applying CSS to web pages built with HTML, you gain precise control over the appearance and feel of the site. CSS is an essential technology in web development and a powerful tool for improving the visual presentation and user experience of web pages.
CSS has the following key features:
CSS Syntax and Formatting Are Simple and Easy
CSS syntax and formatting are truly straightforward. You only need to learn a few basic rules to get started.
A Wide Range of Powerful Style Properties
CSS offers a wide variety of powerful style properties that allow you to style many different aspects of a web page. For example, you can adjust colors, sizes, spacing, text styles, backgrounds, shadows, and more.
And that’s not all — CSS also enables you to create animations.
Enables Responsive Web Design
CSS is also used to implement responsive web design, allowing you to apply styles that adapt to different conditions such as browser size, type, device characteristics, and various media. This enables you to create and adjust web page styles tailored specifically for desktops, mobile devices, and other environments.
CSS Continues to Evolve and Update
CSS is one of the core languages of the open web, which is based on the internet and promotes a free and accessible environment for everyone. The open web aims to be inclusive and participatory, built on web standards and open platforms that ensure compatibility across various operating systems and devices.
Web standards are agreements that define web technologies and protocols, with key standards including HTML, CSS, and JavaScript.
In modern web development, design plays a crucial role. Alongside advances in browsers and technology, CSS continues to evolve and receive updates. Like HTML and other languages, CSS has versioned specifications—CSS1, CSS2.1, and CSS3. The latest version currently in widespread use is CSS3.
There is unlikely to be a CSS4 version in the future. This is because CSS3 is continuously updated, with new or improved features developed and standardized as independent modules whenever needed.
Rather than being developed as a single, comprehensive new version, the concept of CSS4 does not exist. Instead, CSS continues to evolve by adding new features and modules while maintaining the modular development approach introduced in CSS3.
This modular approach enables faster and more flexible updates, allowing browser vendors and developers to adopt and implement necessary features more quickly. Additionally, the modular structure of CSS3 supports the ongoing introduction of new features while preserving compatibility and consistency.
CSS3 itself is an extended version of CSS2, introducing new capabilities within a modular framework where each module can be updated independently. Therefore, the absence of a CSS4 version reflects the continued use of this modular development and update strategy.
For these reasons, the W3C does not increment CSS version numbers but instead provides periodic CSS Snapshots. These Snapshots define the state of the CSS standard at specific points in time. They offer developers and browser vendors clear information about the core features and level of support in the current CSS standard, helping maintain consistent development and compatibility.
CSS Snapshots serve as important reference points to ensure compliance and interoperability in the use and implementation of CSS.