How Text in Elements Becomes Vertically Centered In HTML, the element is commonly used to create buttons that trigger actions or navigate to different web pages. However, there is an intriguing observation about the vertical alignment of text within these buttons. Despite not explicitly specifying any vertical alignment properties, the text in elements consistently appears centered. This article delves into the underlying mechanisms that contribute to this alignment phenomenon. Introducing the Element The element defines a clickable button that can be customized using CSS. It differs from the generic element, which does not have inherent button functionality or specific styling. While it is possible to create buttons using elements, the element provides more accessible and semantically meaningful options. The Hidden Sibling Upon closer inspection of the rendered HTML, it becomes apparent that elements often contain an additional internal element. This element, called "-moz-button-content" in Firefox, resides between the opening tag and the button's child content. It is hidden from the CSS and set to "display: block" without inheriting the height of the itself. The Browser's Hardcoded Alignment The key to understanding the automatic centering of text in elements lies in the browser's inherent behavior. As revealed in the source code of Firefox, the browser has a hardcoded mechanism that centers the content of elements within their allocated space. This built-in logic ensures that regardless of the height of the , its text will always be vertically aligned. Combining Forces The interplay between the hidden sibling and the browser's hardcoded alignment creates the effect of vertically centered text. The extra space introduced by the sibling divides the 's height into two vertical halves. The browser's alignment mechanism then positions the text in the center of this space, effectively aligning it vertically.
