SEO Glossary / CSS (Cascading Style Sheets)

CSS (Cascading Style Sheets)

What is CSS (Cascading Style Sheets)?

CSS, or Cascading Style Sheets, is a stylesheet language used to describe the presentation of a document written in HTML or XML. CSS defines how HTML elements are to be displayed on screen, paper, or in other media, allowing developers to separate content from design for more flexible and efficient web development.

Key Features of CSS

  1. Styling Web Elements: CSS allows you to control various design aspects of web elements, including:

    • Text size and color
    • Font styles
    • Element positioning
    • Spacing (margin, padding)
    • Borders and backgrounds
    • Animations and transitions
  2. Cascading Rules: The term "cascading" refers to the way CSS applies rules. Multiple styles can be applied to the same element, and the browser will determine which style to use based on specificity, importance, and source order.

  3. Separation of Content and Presentation: By keeping the design and layout instructions in separate CSS files, developers can manage and update the visual presentation of multiple web pages more efficiently. This practice also improves the maintainability and readability of the code.

Types of CSS

  1. Inline CSS:

    • Applied directly within an HTML element using the style attribute.
    <p style="color: blue; font-size: 14px;">This is a blue paragraph.</p>
  2. Internal CSS:

    • Defined within a <style> tag in the <head> section of an HTML document.
        p { color: blue; font-size: 14px; }
  3. External CSS:

    • Stored in separate .css files and linked to HTML documents via the <link> tag.
      <link rel="stylesheet" type="text/css" href="styles.css">

Advantages of Using CSS

  1. Consistency:

    • Applying a single CSS file to multiple web pages ensures a consistent look and feel across the entire site.
  2. Efficiency:

    • By separating content from design, CSS allows developers to apply styles globally and update them from a single location.
  3. Improved Performance:

    • External CSS files can be cached by browsers, reducing load times for subsequent page visits.
  4. Enhanced User Experience:

    • CSS enables the creation of responsive designs that adapt to different screen sizes and devices, improving accessibility and usability.

Best Practices for Using CSS

  1. Keep CSS Organized:

    • Use comments and consistent naming conventions to keep your CSS code readable and maintainable.
    • Group related styles together and follow a logical structure.
  2. Use External Stylesheets:

    • Whenever possible, use external stylesheets to keep HTML clean and separate content from presentation.
  3. Leverage CSS Preprocessors:

    • Tools like Sass or LESS can help you write more efficient and maintainable CSS by providing features like variables, nesting, and mixins.
  4. Optimize for Performance:

    • Minify CSS files to reduce file size and improve load times.
    • Avoid redundant or unused styles to keep CSS files lean.


CSS (Cascading Style Sheets) is an essential technology for web development, enabling developers to design and format web pages effectively. By understanding and implementing CSS best practices, you can create visually appealing and user-friendly websites that offer a great user experience across various devices and browsers.

For more information on CSS and advanced techniques, consider exploring MDN Web Docs on CSS.