Why Doesn\'t \'Margin: Auto\' Center Elements Vertically?

Centering Elements Vertically with "Margin: Auto"

While "margin: auto" effectively centers elements horizontally, its vertical alignment capabilities may be limited. This is due to the way block boxes are stacked vertically and the potential for margin collapse.

According to CSS2.1 section 10.6.2, block boxes are stacked from top to bottom in normal flow. Vertical margins may collapse, zeroing out in certain circumstances. In cases where the containing block has an auto height and only one block box, its top and bottom margins are inherently zero.

For multiple block boxes in the same flow or out-of-flow boxes affecting in-flow layout, resolving auto margins becomes more complex. This extends to inline elements and floats, where auto left and right margins are set to zero to avoid interferences with line boxes.

In contrast, absolutely positioned boxes are oblivious to other boxes in the same positioning context. Hence, auto top and bottom margins can be calculated for them based solely on their containing blocks.

Flexbox provides a unique solution to flex items that are fully aware of each other within the flex formatting context. Vertical margins in flexbox follow distinct rules, allowing for more precise control over element alignment.

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