What determines style rule precedence in CSS?

The determination of style rule precedence in CSS is primarily regulated by the specificity of the selectors used. When multiple rules apply to the same HTML element, CSS uses a specificity hierarchy to decide which style to apply.

Specificity is calculated based on the types of selectors: inline styles have the highest specificity, followed by IDs, classes, attributes, and then element selectors. For example, an inline style applied directly to an element will override styles defined in a stylesheet due to its higher specificity. When the specificity is the same among competing styles, the one defined last in the CSS source order will take precedence.

This principle is fundamental in ensuring that the most relevant styles for an element are applied correctly without ambiguity in complex stylesheets. Understanding specificity helps in managing and writing CSS effectively to achieve desired styling outcomes.