what is css – Dessign

Updated: Jul 3, 2023 By: Dessign Team

how does CSS works

Cascading Style Sheets, commonly known as CSS, play a vital role in web development. This rule-based language allows developers to define styles and control the visual appearance of HTML elements on web pages. By specifying groups of styles, developers can effortlessly apply design elements to various parts of a website, enhancing its aesthetics and user experience.

CSS works by combining a document’s content with its style information. When a browser loads a webpage, it processes the HTML content and applies the CSS styles accordingly. This ensures that the layout and design of the page are displayed consistently across different devices, browsers, and screen sizes.

The latest version, CSS 3, has introduced new features and capabilities, such as advanced selectors, animations, and responsive design. These enhancements allow developers to create striking, efficient, and accessible web content that caters to a diverse range of users and preferences.

The Basics of CSS

What Is CSS

CSS, or Cascading Style Sheets, is a style sheet language used for describing the presentation of a document written in markup languages like HTML. This language allows web developers to control the visual appearance and layout of web pages by applying various styles, such as colors, fonts, and spacing, among other things.

How CSS Works

CSS works by defining rules and applying styles to specific HTML elements or groups of elements on a web page. A CSS rule consists of a selector, which identifies the target element(s), and a set of declarations, which describe the styles to be applied. For example, a developer could create a rule to display the main heading as large, bold, and red text. The rule-based nature of CSS allows for efficiency and consistency in web design, as styles can be reused and applied to multiple elements or pages.

Difference Between HTML and CSS

Difference Between HTML and CSS

While HTML and CSS are closely related, they serve distinct purposes. HTML is the foundation of a website, providing its content and basic structure through elements such as headings, paragraphs, lists, and links. On the other hand, CSS is responsible for the aesthetics and overall visual design, allowing for customization of the appearance of HTML or HTML5 elements.

In summary, HTML focuses on the content and structure of a web page, while CSS enhances the design and presentation. By separating these concerns, developers can create web pages that are both visually appealing and easy to maintain.

CSS Syntax and Structure

CSS (Cascading Style Sheets) is a powerful styling language used to enhance the appearance of HTML markup, making it easier to create visually appealing web pages. In this section, we will discuss the syntax and structure of CSS, focusing on its foundational elements: Selectors, Properties, Declarations, and Values.


Selectors are the key components in CSS that allow us to target specific HTML elements and apply styles. They come in various formats, including element type, class, and ID selectors. Element type selectors target a specific HTML tag (e.g., ph1div). Class selectors target elements belonging to a specific class (e.g., .intro). ID selectors target unique elements based on their id attribute (e.g., #navbar). Enabling more complex targeting, combinators like the descendant, adjacent sibling, and general sibling selectors can be used in conjunction with other selectors source.


Properties define the visual aspect of an HTML element that you want to modify. Some common properties include colorfont-sizebackground-colorwidth, and height. Properties are paired with values to create a declaration, determining how an element appears on a web page source.


A CSS declaration is the combination of a property and its corresponding value, separated by a colon (:) and ending with a semicolon (;). Declarations are contained within a CSS rule, which consists of a selector and one or more declarations enclosed in curly braces (). For example:

    color: red;
    font-size: 16px;

In this example, color: red; and font-size: 16px; are declarations, while p is the selector source.


Values specify the desired appearance of a property and determine how that property is rendered on the web page. Most properties accept a range of values, either as predefined keywords (e.g., leftrightcenter), units (e.g., px%em), or color codes (HEX, RGB, or HSL). For example, in the declaration font-size: 16px;16px is the value assigned to the font-size property source.

By understanding the concepts of selectors, properties, declarations, and values, web developers can effectively utilize CSS to create visually appealing and well-structured web pages.

CSS Styling and Presentation

CSS Styling and Presentation

Fonts and Text

CSS allows you to control the presentation of your website’s text through various properties such as fontfont-size, and font-family. By specifying these properties, you can achieve a consistent text styling across all elements and pages. For example:

  font-size: 2em;
  font-family: Arial, sans-serif;

Colors and Backgrounds

Handling both text and background colors with CSS is simple using the color and background-color properties. You can apply these styles to specific elements or within the entire website:

  color: #333;
  background-color: lightgray;

Boxes, Borders, and Spacing

CSS provides a flexible box model management system to control the layout and spacing of elements on your webpage. With properties like boxborderwidth, and spacing, you have fine-grained control over the dimensions and presentation of elements. For example:

  width: 50%;
  border: 1px solid #ccc;
  margin: 10px;
  padding: 20px;

Layout and Positioning

To arrange elements on your web page, CSS offers various layout techniques. These techniques provide control over elements based on their default positions, relationships to other elements, parent containers, and viewport or window. Layout and positioning can be achieved by utilizing properties such as displayfloatposition, and flex.

Types of CSS

Types of CSS

CSS (Cascading Style Sheets) plays a crucial role in the relationship between HTML and visual representations of a site. There are three types of CSS used in web designing: Inline Styles, Internal Stylesheets, and External Stylesheets.

Inline Styles

Inline Styles are applied directly to HTML elements using the style attribute. This method allows targeting specific elements of a webpage, providing a fast and easy way to apply customized styling to individual components. However, inline styles can lead to cluttered HTML code, as they require repetitions of style declarations for each element that needs styling. For example:

<p style="color: blue; font-size: 14px;">This is an inline styled paragraph.</p>

Internal Stylesheets

Internal Stylesheets are included directly within the <head> section of an HTML document and apply to the entire document. This method keeps styling information separate from the content, making it easier to maintain and control the visual appearance of a site. Internal stylesheets utilize <style> elements and can define multiple style rules for a variety of components, like this:

      color: blue;
      font-size: 14px;

External Stylesheets

External Stylesheets store CSS properties in a separate .css file and are linked to the HTML document using a <link>tag. This method promotes a cleaner and more organized structure, as CSS rules can be set once and applied to numerous web pages. By keeping the style sheet and HTML code separate, it becomes more manageable and efficient, especially for large websites. An example of an external stylesheet linking is shown below:

  <link rel="stylesheet" href="https://dessign.net/what-is-css/styles.css">

And in the styles.css file:

  color: blue;
  font-size: 14px;

Each CSS type has its own advantages and use cases, but the use of external stylesheets is generally recommended for larger web projects due to its scalability and maintainability.

CSS and Web Browsers

CSS and the DOM

CSS, or Cascading Style Sheets, is a stylesheet language used to describe the presentation of a document written in HTML or XML. When a web browser loads an HTML file, it also looks for a CSS file to apply styles to the elements on the page. The browser parses the fetched CSS and sorts the different rules by their selector types (such as element, class, ID) into different “buckets.” Based on the selectors it finds, the browser then works out which rules should be applied to which nodes in the DOM, attaching style to them as required. This intermediate step is called a render tree1.

Browser Support

In modern web development, it’s important to consider that different web browsers might support various CSS features to varying extents. Ensuring that your CSS code is compatible with major browsers (such as Chrome, Firefox, Safari, and Edge) is crucial to provide a consistent user experience across different devices and platforms. You can check for browser support and compatibility using resources like Can I Use which informs you about the support status of specific CSS properties and features in various web browsers.

Default Styles

Web browsers also come with their default styles for certain HTML elements, such as headings, paragraphs, lists, and tables. These built-in styles can sometimes result in inconsistencies in the appearance of a webpage across different browsers. To counteract this, developers often use a reset stylesheet or a CSS framework (like Normalize.css) to ensure a consistent starting point, by overriding default browser styles with custom styles that are applied uniformly across all browsers2.

Working with Responsive Design

Responsive design is essential in modern web development, as it ensures that websites look good on a variety of devices and screen sizes. This approach automatically adapts the content to fit the viewer’s screen, whether it’s on a tablet, phone, television, or watch. In this section, we’ll discuss media queries, adapting to different devices, and CSS frameworks.

Media Queries

Media queries are the foundation of responsive design, as they allow developers to apply different CSS styles based on the characteristics of the user’s device, such as screen size, resolution, and orientation. These queries are created using the @media rule, which defines a set of conditions that must be met for the enclosed CSS styles to be applied. For example, to style elements differently on small screens, a developer might use:

@media (max-width: 768px) 
  /* CSS rules for smaller screens go here */

Adapting to Different Devices

In order to create a truly responsive design, it’s important to consider the wide range of devices on which users might view your website. This includes not only considering different screen sizes, but also taking into account factors such as device orientation, resolution, and color capabilities.

One key aspect of designing for different devices is setting the viewport, which determines the initial scale and dimensions of a web page when it’s loaded on a mobile device. This can be done by adding a <meta> element to the HTML head, like so:

<meta name="viewport" content="width=device-width, initial-scale=1">

With the viewport properly set, it’s much easier to create a design that adapts to a variety of screens and devices.

CSS Frameworks

Developers often use CSS frameworks to streamline their work and ensure a consistent, attractive design across various devices. These frameworks can save time and effort by providing pre-made design components that are already optimized for responsive design. Some popular CSS frameworks include Bootstrap, Foundation, and Bulma. By using these tools, developers can create cohesive, professional-looking websites that adapt seamlessly to different devices and screen sizes.

In conclusion, responsive design is crucial for creating websites that look and function well on a range of devices. By using media queries, adapting to different devices, and employing CSS frameworks, developers can build websites that are user-friendly, visually appealing, and functional on any screen.

Advanced CSS Features

Animations and Transitions

CSS provides powerful tools for creating animations and transitions to enhance the user experience on websites. Animations involve changing an element’s appearance over time, while transitions smooth the progress of an element’s style change from one state to another. With CSS animations and transitions, designers can create engaging and interactive web content, making elements like buttons, menu items, and images more dynamic as users interact with them.

To create animations, CSS leverages the @keyframes rule, defining the behavior and duration of the animation. Transitions, on the other hand, use properties like transition-propertytransition-duration, and transition-timing-function to achieve the desired effect. These features can create complex effects without needing additional JavaScript or libraries, achieving a more performant and lightweight web experience.

CSS Modules

CSS Modules address the challenges of global styles and unintentional style clashes in modern web development. Instead of using global scope, CSS Modules rely on locally scoped CSS for each module, enabling developers to create component-specific styles without risk of affecting other sections of a website.

To use CSS Modules, you need to install them as a dependency and configure your project’s build system, such as Webpack or Babel, to support them. Once set up, you can create separate files for your modules, referencing them in your JavaScript (or framework of choice) to import and apply styles to specific components.

CSS Modules are especially useful in the context of component-based frameworks, like React or Vue.js, where the encapsulation of styles and functionality within components is crucial for maintainability and modular development.

In summary, advanced CSS features like animations, transitions, and modules enhance the appearance and functionality of websites. These features allow for more interactive user experiences and improved development practices by isolating styles to specific components.

CSS Best Practices and Resources

Code Organization

Organizing your CSS code is essential for maintaining clean and efficient stylesheets. Web developers can benefit from following a few best practices, such as:

  • Modularize: Break your CSS into smaller, modular files that can be imported into a main stylesheet. This helps to maintain separation of concerns and reduces clutter.
  • Use comments: Comments are invaluable to provide context and explanations for your code. Use them generously to describe each section, module, or complex rule.
  • Consistent naming conventions: Stick to a naming convention for your classes, such as BEM (Block Element Modifier), to enhance readability and maintainability.

Resources for Learning and Improving CSS

Whether you’re just starting out or looking to advance your CSS skills, there are plenty of resources available:

  • MDN Web Docs: A comprehensive resource provided by Mozilla, covering everything from CSS basics to advanced techniques. It contains a wealth of tutorials organized according to experience level, making it an excellent starting point for learners of all stages.
  • W3C: The World Wide Web Consortium (W3C) is the international organization responsible for developing web standards, including CSS. W3C offers a variety of resources and documentation to help web developers understand and implement CSS effectively.
  • CSS-Tricks: A popular blog and resource site that covers all aspects of web development, with a strong emphasis on CSS. This site features articles, tutorials, and guides on a wide range of CSS topics, from beginner to advanced.

Overall, mastering CSS requires practice and dedication. By following best practices, leveraging available resources, and continuously learning, web developers can enhance their CSS skills and build more efficient and aesthetically pleasing websites.

Frequently Asked Questions

What are the main components of CSS?

CSS, or Cascading Style Sheets, is a rule-based language consisting of selectors, properties, and values. Selectors target specific HTML elements on a web page, while properties and values determine the styling of those elements. For example, setting the color property to red changes the text color of the targeted element to red.

How does CSS interact with HTML?

CSS interacts with HTML by applying styles to elements within an HTML document. Developers link CSS to the HTML document using the <link> tag in the <head> section or by directly embedding the CSS within the HTML using <style>tags. CSS reads the HTML structure and applies the specified styles to the corresponding elements, thus enhancing the visual appearance of the web page.

What are the advantages of using CSS?

Using CSS offers several advantages, including improved website design consistency, easier site maintenance, and faster loading times. CSS allows developers to control the layout and styling of multiple web pages simultaneously through external stylesheets. It also separates the content (HTML) from the presentation (CSS), making it easier to update the site’s design without altering the underlying HTML.

Can you explain the different types of CSS?

CSS can be implemented in three ways: inline, internal, and external. Inline CSS applies styles directly to HTML elements using the style attribute. Internal CSS places styles within <style> tags in the <head> section of an HTML document. External CSS entails creating a separate (.css) file that contains all the styles and is linked to the HTML document using the <link> tag. External CSS is the recommended method, as it promotes easier maintenance and better separation of concerns.

What are some common CSS properties?

Common CSS properties include colorbackground-colorfont-familyfont-sizemarginpaddingborder, and display. These properties allow developers to control text colors, background colors, font choices, spacing, and layout of various HTML elements on a web page.

How do percentage values work in CSS?

Percentage values in CSS allow for relative sizing and positioning of elements based on the dimensions of their parent element. For example, setting an element’s width property to 50% will make the element occupy half of its parent element’s width. Using percentage values makes it easier to create responsive designs that adapt to different screen sizes and orientations.