Instruction: Discuss the cascading nature of CSS Custom Properties and its implications on their scope within a document.
Context: This question evaluates the candidate's understanding of CSS Custom Properties (variables), focusing on their cascading nature and scope.
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CSS custom properties cascade in the same way that other CSS properties do. This means they are applied according to the Cascade and Inheritance principles inherent to CSS. The value of a CSS variable can be defined or redefined at any point in a stylesheet, and its scope is determined by the selector where it is defined. Essentially, a CSS variable will be available for use within the element it's defined on, as well as any of its child elements, unless overridden by a more specific selector.
For example, if you define a custom property at the root level using :root { --main-color:...