Why Doesn\'t a Button Expand to Fill Its Container with `display: block` and `width: auto`?

Why Doesn't "display: block" & "width: auto" Expand a Button to Fill the Container?

In HTML, certain elements, such as buttons, inputs, selects, and images, are designated as "replaced elements." These elements have inherent dimensions and appearances determined by external resources, such as operating system or plugins.

When you apply "display: block" to a button, it indicates that the button should behave like a block-level element and occupy the full width of its container. However, "width: auto" specifies that the button's intrinsic width should be used.

Replaced elements possess intrinsic dimensions, meaning their width and height are fixed and cannot be modified by CSS. For instance, an image element's intrinsic dimensions are determined by the size of the image file. When "width: auto" is applied to a replaced element, the browser respects its intrinsic width.

Additionally, replaced elements may have visual formatting requirements imposed by the browser or operating system that override CSS styling. Buttons, for example, have built-in user interface controls that cannot be modified solely through CSS.

In the case of buttons, while not officially defined as a replaced element by W3C, it exhibits similar behavior. Hence, applying "display: block; width: auto;" to a button will not stretch it to fill the container because its intrinsic width is constrained by the button's visual formatting requirements.

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