Which CSS property should you use to add space between a border and its content?

The correct property to use for adding space between a border and its content is padding. Padding creates space inside an element, pushing the content away from the border. This means that any content within the element will have a gap between it and the border, making the layout cleaner and enhancing readability.

Understanding why padding is used specifically for this purpose is essential. When you apply padding, it increases the dimension of the element without altering its outer boundaries, as the padding is added inside the element. This internal spacing ensures that the border encapsulates the content effectively while providing a clear separation.

In contrast, other properties such as margin create space outside an element, affecting the distance between it and surrounding elements rather than within itself. Border-spacing is specific to tables and manages the space between borders of adjacent cells, which does not apply to content directly within a standard block element. The property named 'spacing' does not exist in CSS, making it an invalid option for this context.