Why Doesn\'t \'margin: auto\' Vertically Center Elements?

Vertical Centering Conundrum with "margin: auto"

In the world of CSS, the "margin: auto" property is a popular tool for horizontally centering elements. However, when it comes to vertical alignment, it often falls short.

As evident in the provided example, a blue div with "margin: auto" is effortlessly centered horizontally, but remains unadjusted vertically. The reason lies in the specifications of CSS2.1 (section 10.6.2).

In block layouts, elements are stacked vertically, and margins may collapse. For a standalone block box with automatic height and a bordered parent, the margins are naturally zeroed out. However, when multiple block boxes are introduced or additional elements impact layout (e.g., clearance), auto margins become ambiguous and need further resolution.

Similarly, inline elements (including atomic inlines) and floats cannot vertically center with auto margins due to their specific layout rules. However, absolutely positioned boxes have no such limitations as they are not affected by other elements within their positioning context. Flexbox, on the other hand, offers a different approach to layout, allowing the auto margins of flex items to be calculated with respect to the flex container due to their inherent awareness of other flex items.

Therefore, while "margin: auto" effectively centers elements horizontally, it falls short in vertical centering due to the complexities of block layout and the ambiguities that arise when multiple elements are involved.

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