Which CSS property determines the horizontal alignment of a block-level element?

The property that determines the horizontal alignment of a block-level element is actually the 'float' property. The 'float' property can be used to push a block-level element to the left or right of its container, allowing surrounding text or inline elements to wrap around it. When you set an element to float, it takes the element out of the normal document flow and aligns it accordingly.

In contrast, 'text-align' primarily affects the alignment of text and inline elements within a block container rather than the block-level element itself. 'Vertical-align' is used to control the vertical alignment of inline or table-cell elements, and 'width' defines the size of an element but does not determine its alignment.

Understanding the specific functions of these properties helps clarify their uses in layout design, particularly in CSS.