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Introduction to CSS

A comprehensive overview of CSS, its purpose, and how it interacts with HTML.

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Introduction to CSS

What is CSS?

CSS stands for Cascading Style Sheets. It is a stylesheet language used to describe the presentation of a document written in HTML (or XML). Essentially, CSS controls the look and feel of your website, separating the content (HTML) from the styling.

The Purpose of CSS

The primary purpose of CSS is to define how HTML elements should be displayed. This includes things like:

  • Colors: Setting the text color, background color, and border colors of elements.
  • Fonts: Specifying the font family, font size, font weight (boldness), and font style (italic).
  • Layout: Controlling the positioning of elements on the page, including margins, padding, and alignment.
  • Responsiveness: Adapting the website's layout to different screen sizes and devices.
  • Visual Effects: Adding shadows, transitions, animations, and other visual enhancements.

By using CSS, you can create visually appealing and user-friendly websites.

How CSS Works with HTML

CSS works by applying rules to HTML elements. These rules consist of a selector that identifies the element(s) to be styled and a declaration block that contains one or more properties and their corresponding values.

Here's a simple example:

 /* CSS Rule */
          h1 {
            color: blue;
            text-align: center;
          }

In this example:

  • h1 is the selector. It targets all <h1> elements on the page.
  • The code within the curly braces {} is the declaration block.
  • color is a property, and blue is its value. This sets the text color of all <h1> elements to blue.
  • text-align is another property, and center is its value. This centers the text within all <h1> elements.

CSS can be applied to HTML in three main ways:

  1. Inline CSS: Styles are applied directly within the HTML element using the style attribute. (Generally avoided except for very specific and isolated cases.)
  2. Internal CSS: Styles are defined within a <style> tag in the <head> section of the HTML document. (Useful for smaller projects or page-specific styling.)
  3. External CSS: Styles are written in a separate .css file and linked to the HTML document using the <link> tag. (The preferred method for larger projects, as it promotes code reusability and maintainability.)

For example, to link an external CSS file named "styles.css", you would add the following line to the <head> of your HTML document:

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

Cascading Nature of CSS

The "Cascading" in CSS refers to the way that styles are applied to elements when multiple style rules conflict. The browser uses a specific order of precedence to determine which style rule takes effect. Generally, the order is:

  1. Inline Styles: Styles applied directly within the HTML element have the highest precedence.
  2. Internal Styles: Styles defined within the <style> tag.
  3. External Styles: Styles defined in linked CSS files.
  4. Browser Default Styles: The browser's default styles for HTML elements have the lowest precedence.

Within each of these levels, specificity also plays a role (more specific selectors override less specific ones), and the order in which the rules are defined also matters (later rules override earlier rules, assuming equal specificity).

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