Which CSS property controls the space inside an element?

The padding property controls the space inside an element. It is used to create space between the content of the element and its border. When you apply padding, you can specify the amount of space on all sides (top, right, bottom, and left) of the content. This internal space is critical for improving readability and design aesthetics since it prevents the content from touching the edges of the element, making it look more visually appealing.

The other properties mentioned, while related to layout, serve different purposes. The margin property affects the space outside an element, creating distance between it and neighboring elements. The border property defines the outer edge of the element, visually framing it. The spacing property does not exist in standard CSS, making it a non-option in this context.