What does the CSS position: relative; do?

The declaration CSS position: relative; modifies the positioning of an element in relation to its original place within the document's flow. When an element is assigned this property, it retains its position in the layout, but the coordinates defined by properties like top, right, bottom, and left allow for adjustments from its original position.

For instance, if you apply a top style of 10 pixels, the element moves down 10 pixels from where it would normally be positioned, but the space it originally occupied remains reserved in the layout. This means that while you can visually shift the element around, the overall layout structure, including other elements, stays consistent as if the element were still in its original location.

Understanding this behavior is crucial as it allows for nuanced control over layout without disrupting the document flow, which is essential for effective web design.