What is the primary purpose of the CSS margin property?

The primary purpose of the CSS margin property is to create space outside an element. This means it is used to define the distance between the element's outer edge and the edges of surrounding elements or the viewport. When you apply margins, you are effectively pushing other elements away and positioning the element in relation to its neighbors, which is essential for layout control.

Margins can be set individually for each side of an element (top, right, bottom, left), and they can also collapse under certain circumstances, which is an important aspect of how margin behaves compared to padding, which creates space inside an element. This distinction helps to clarify the visual separation between elements in a web layout, enhancing the overall user experience and design aesthetics.

The other options do not accurately define the function of the margin property. For instance, creating space within an element is achieved using the padding property, changing the size of an element can be done using the width or height properties, and setting an element's visibility refers to the visibility property rather than margin. Thus, margins specifically address the space outside an element, reinforcing their unique role in CSS layout management.