Why Doesn\'t `display: block` Make My Input Element Fill Its Container\'s Width?

Input Element Not Expanding to Block Container Width with 'Display:block'

Despite assigning 'display:block' to an input element, it may not behave like a div and fill the container width. This deviation stems from the inherent behavior of input elements in CSS.

In CSS, 'display:block' typically allows an element to expand and take up the full available width. However, input elements are designed to have 'display:inline' as their default display mode. This means they will only take up the width of their content, which includes any padding and borders.

To resolve this issue and force the input element to fill the width, one can use 'width:100%'. However, this approach can be problematic if the input has non-zero padding and border, as it will result in a final width that exceeds 100%.

Cross-Browser Solution Using CSS3 'box-sizing'

A comprehensive solution involves using the relatively unknown 'box-sizing:border-box' property from CSS3. This property ensures that the width of the input element (or any other element) includes its padding and border.

Here's a modified version of the CSS code provided:

form { display: block; margin: 0; padding: 0; width: 50%; border: 1px solid green; overflow: visible }
div, input { display: block; border: 1px solid red; padding: 5px; width: 100%; font: normal 12px Arial; }

.bb {
    box-sizing: border-box; /* CSS 3 rec */
    -moz-box-sizing: border-box; /* Firefox 2 */
    -ms-box-sizing: border-box; /* Internet Explorer 8 */
    -webkit-box-sizing: border-box; /* Safari 3 */
    -khtml-box-sizing: border-box; /* Konqueror */
}

By adding the '.bb' class to the input element, you can enable 'box-sizing:border-box' for cross-browser compatibility. This ensures that the input element will always take up the full available width, regardless of its padding and borders.

Additional Notes:

1. Internet Explorer 6 and 7 do not support CSS3 'box-sizing', but it can be enabled using a behavior script.
2. The 'box-sizing:border-box' property is supported in most modern browsers, including Google Chrome, Firefox, Safari, and Opera.

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