CSS Structure
CSS, which stands for Cascading Style Sheets, is a language used to control the presentation and layout of HTML elements on a web page. While HTML provides the structure and content, CSS is what gives a website its look and feel—things like colors, fonts, spacing, and positioning. The structure of CSS is fairly straightforward once you get the hang of it. A CSS rule set is made up of two main parts: the selector and the declaration block. The selector targets the HTML element you want to style, and the declaration block contains one or more declarations enclosed in curly braces {}. Each declaration consists of a property and a value, separated by a colon. For example, p { color: blue; font-size: 16px; } is a rule that tells the browser to display all paragraph (<p>) text in blue, with a font size of 16 pixels. Declarations are separated by semicolons, and while one-line styles are common, you can also break them up into multiple lines for better readability. CSS can be written in three different ways: inline, internal, or external. Inline CSS is added directly into an HTML element using the style attribute, like <p style="color: red;">Text</p>. Internal CSS is placed inside a <style> tag within the <head>
section of your HTML document. External CSS, which is the most common and recommended method for larger projects, involves writing all your CSS rules in a separate .css file and linking it to your HTML using a <link> tag. This approach keeps your code organized and easier to maintain. CSS also allows you to group selectors to apply the same styles to multiple elements, like h1, h2, h3 { font-family: Arial; }, which sets the same font for all heading levels. Beyond basic styling, CSS provides powerful tools for layout and positioning. You can use the box model, which includes content, padding, border, and margin, to control spacing around elements. Layout techniques such as Flexbox and Grid allow for complex, responsive designs that adjust to different screen sizes. CSS also supports pseudo-classes like :hover or :focus, which apply styles when a user interacts with an element, as well as media queries that change styles based on screen size, making your design more mobile-friendly. Variables, introduced in modern CSS, let you define custom values that can be reused throughout your styles, helping keep code cleaner and more manageable. For example, you can define a color variable with --main-color: #3498db;
and use it later like color: var(--main-color);. The “cascading” part of CSS means that when multiple rules apply to the same element, the browser decides which one to use based on specificity, importance, and source order. This structure gives you precise control over how elements appear and behave on the page. In short, CSS’s structure is designed to be readable, flexible, and powerful, making it an essential tool for anyone creating or styling websites.
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