Which snippet of CSS is commonly used to center an element horizontally?

The snippet that is commonly used to center an element horizontally is margin: 0 auto;. This CSS rule sets the top and bottom margins to 0 and the left and right margins to auto. When an element has a defined width, using auto for the left and right margins allows the browser to calculate and distribute the remaining horizontal space equally on both sides, effectively centering the element within its containing block.

This method is particularly effective for block-level elements, as it ensures that the element will be centered regardless of the screen size or containing element width, as long as the element's width is less than that of its parent. It's a straightforward and widely accepted approach in CSS layouts.