CSSregler

CSSregler, or CSS rules, are the fundamental building blocks of Cascading Style Sheets. A CSS rule is composed of two main parts: a selector and a declaration block. The selector specifies which HTML element(s) the style should be applied to. Examples include type selectors like `p` for paragraphs, class selectors like `.my-class` for elements with a specific class attribute, and ID selectors like `#unique-id` for elements with a unique ID. Selectors can also be combined to target more specific elements.

The declaration block contains one or more declarations, each consisting of a CSS property and its corresponding value. Declarations are separated by semicolons, and the entire block is enclosed in curly braces. For instance, `color: blue;` is a declaration where `color` is the property and `blue` is the value. Properties control various aspects of an element's appearance, such as its text color, font size, background, margins, and borders.

When a browser renders an HTML document, it uses CSS rules to determine how each element should be displayed. The "cascading" aspect refers to the hierarchy and order in which these rules are applied, with more specific rules or rules defined later in the stylesheet taking precedence. Understanding CSS rules is essential for anyone learning to style web pages.