The Cascade, Specificity, and Inheritance
Other than being the C in the acronym CSS, the fact that style sheets are described as “cascading” is an important, if complex, part of the way styles are applied to the elements in a document. It’s called the CSS cascade, because style declarations cascade down to elements from many origins.
The cascade combines the importance, origin, specificity, and source order of the applicable style declarations to determine exactly—and without conflict—which declaration should be applied to any given element.
Inheritance is the means by which, in the absence of any specific declarations applied by the CSS cascade, a property value of an element is obtained from its parent element.