The cascading order in CSS is a fundamental concept that determines how styles are applied to HTML elements when there is more than one rule that could apply. It's essential to understand this order to effectively style web pages and ensure that the desired design is achieved.

Specificity in CSS

Specificity is a key factor in the cascading order. It refers to the weight given to a given CSS declaration, based on the form of the selector used to target the element. In essence, it's a measure of how specific a selector is, and thus, how much priority it should be given when applying styles. The specificity hierarchy is as follows:

1. Inline styles, added directly to HTML elements with the style attribute, have the highest specificity.

2. IDs are more specific than classes and attribute selectors.

3. Classes, attributes, and pseudo-classes come next.

4. Element and pseudo-element selectors have the lowest specificity.

Here's an example to illustrate specificity: