Εξηγήστε πώς ο περιηγητής καθορίζει σε ποια στοιχεία πρέπει να εφαρμοστούν τα CSS στυλ.

The browser determines which elements to apply CSS styles to by using search and matching mechanisms based on CSS selectors.

The process occurs as follows:

1. CSS Parsing: The browser parses CSS files and <style> blocks in HTML, creating an internal representation of styles.
2. HTML Parsing: The browser parses HTML and creates the DOM (Document Object Model) tree.
3. Matching: For each node in the DOM tree, the browser attempts to match it with CSS rules. This is done by checking the selectors in the CSS rules. Usually, the browser works from more specific parts of the selector to less specific parts (right to left). For example, for the selector div article p, it first finds p, then checks if it is a descendant of article, which in turn is a descendant of div.
4. Applying: If a DOM node matches one or more CSS rules, the browser applies the corresponding styles to that node. In case of multiple applicable rules, the browser determines the final set of styles using specificity rules, declaration order, and inheritance.

Specificity:

Specificity is an algorithm used by the browser to calculate the weight of a CSS selector. A more specific selector has higher priority when applying styles. Specificity is calculated based on the number of ID, class/pseudo-class/attribute, and element/pseudo-element in the selector.

// a = number of IDs
// b = number of classes, pseudo-classes, attributes
// c = number of elements, pseudo-elements
// Inline styles have the highest priority (1, 0, 0, 0)
// The selector `*` has specificity (0, 0, 0)

Example of specificity calculation:

• p: (0, 0, 1)
• .class: (0, 1, 0)
• #id: (1, 0, 0)
• div p: (0, 0, 2)
• div .class: (0, 1, 1)

Declaration order:

If two rules have the same specificity, the one declared last in the CSS code is applied.

Inheritance:

Some CSS properties are inherited from parent elements to child elements (e.g., color, font-family). If a property does not have an explicit value set on an element, the browser searches for an inherited value upward through the DOM tree.

Thus, the browser determines styles for an element by matching selectors, resolving conflicts using specificity and declaration order, and considering inheritance.