CSS (Cascading Style Sheets) is the language used to control the presentation, layout, and visual aesthetic of a website. While HTML provides the "skeleton" (structure and content), CSS provides the "skin"—defining colors, fonts, spacing, and how elements are positioned across different screen sizes.
Core Functions of CSS
- Visual Styling: Customize text (size, weight, font-family), background colors, and borders.
- Layout Design: Use modern systems like Flexbox for one-dimensional layouts or CSS Grid for complex two-dimensional structures.
- Responsive Design: Through media queries, CSS allows a single webpage to adapt its layout for mobiles, tablets, and desktops.
- Animations and Effects: Create smooth transitions, hover effects, and keyframe animations without needing complex scripts.
How to Implement CSS
There are three primary ways to add CSS to a web project:
- External CSS: Styles are kept in a separate
.css file linked in the <head> of the HTML. This is the most efficient method for large projects because one file can style an entire website. - Internal CSS: Styles are written inside a
<style> tag within the HTML document's <head>. Best for single-page designs. - Inline CSS: Styles are applied directly to an individual HTML element using the
style attribute. This is generally avoided except for quick fixes.
Key Concepts for Designers
- The Box Model: Every element is treated as a box consisting of content, padding, border, and margin.
- The Cascade: Determines which style rule "wins" when multiple rules apply to the same element, based on importance, specificity, and source order.
- Selectors: Patterns used to target specific HTML elements (e.g.,
p for paragraphs, .header for a class, or #logo for a unique ID).
Advantages
- Separation of Concerns: Keeps design code separate from content, making it easier to maintain.
- Consistency: Ensure the same branding (fonts/colors) is applied across every page.
- Performance: Browsers can cache external CSS files, leading to faster load times for returning visitors.
