Why Don\'t Block-Level Input Elements Always Fill Their Containers Like Divs?

Input Elements Displayed as Block: Why They Differ from Divs

It is common to perceive an input element with display: block and width: auto to behave akin to a div, occupying the full width of its container. However, as observed in the given code snippet, this is not the case.

Understanding the Discrepancy

Unlike divs, input elements follow a different box model, known as the border-box model. This model considers padding and borders in the overall width calculation, unlike the content-box model used for divs.

Overcoming the Issue

To force an input element to span the full container width, while respecting its padding and borders, one can employ the max-width: 100% property. This technique essentially constraints the width of the input element to its parent container, even if the computed width exceeds this value due to its border and padding.

Cross-Browser Compatibility

To achieve consistent behavior across browsers, the recently introduced box-sizing: border-box property can be used. This property explicitly instructs the browser to use the border-box model for the target element, irrespective of its default box model.

Implementation

The following code demonstrates this solution:

<div class="wrapper">
  <input type="text" class="input" placeholder="Input Text" />
</div>

<style>
  .wrapper {
    width: 500px;
    border: 1px solid black;
    padding: 20px;
  }

  .input {
    width: 100%;
    box-sizing: border-box;
  }
</style>

This approach ensures that the input element occupies the full width of the container in all major browsers.

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