Why Does Text in `` Elements Automatically Center Vertically?

The Enigma Behind Vertically Centered Text in Elements

The

element exhibits a peculiar behavior: its text content effortlessly centers itself vertically within the element. What seems like a trivial task becomes a mystery when it comes to the

element, where text alignment properties don't seem to have the same effect.

Diving into the Browser Code

To unravel this mystery, we delve into the depths of the Firefox source code, where we stumble upon a crucial piece of information. Firefox employs an intermediary element, labeled as "moz-button-content," which lies between the

tag and its children. This element is set to "display: block" and lacks an explicitly defined height, inheriting only the line-height of the contained text by default.

The Magic Behind Vertical Text Alignment

The core of the mystery unfolds in the browser's hardcoded vertical positioning mechanism for

content. We discover a snippet within the Firefox source code that explicitly places the child element (the "moz-button-content") within a designated extra space within the button's frame.

The Visualized Mystery

Visualizing the

element's layout provides a clearer understanding of the interplay between elements:

+--+-----------------------+^
|  + button extra space     | |
|  |                       | |
+--+-----------------------+ |
|| ::moz-button-content || | button height
||   display: block;    || |
+--+-----------------------+ |
|  |                       | |
|  + button extra space     | |
+--+-----------------------+v

When the

element is provided with a fixed height, the "moz-button-content" element, by virtue of its "display: block" property, assumes the height of its content (typically the line-height of the text). This leads to a deliberate distribution of extra space above and below the content, resulting in the observed vertical centering behavior.

Drawing Parallels between Elements

In contrast, the

element lacks such built-in vertical text centering. To achieve similar alignment behavior, one would need to toggle the "line-height" property of the content or use a specific text alignment property like "flexbox" with "align-items: center."

Dispelling the Illusion

The curious case of the vertically centered text in

elements is thus solved, revealing a harmonious interplay of browser-defined elements and hardcoded text placement. It remains a testament to the intricacies and potential hidden mechanics within seemingly simple HTML tags.

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