How do I get an `` element to fill the available space with `width: auto`?

What does width: auto Mean for Elements?

Despite its common understanding as a directive to fill available space for block elements, width: auto behaves differently for fields.

Definition of width: auto

The CSS specification does not explicitly define the specific behavior of width: auto for elements. However, it generally signifies that the browser should calculate the width based on an element's intrinsic properties.

Achieving Desired Behavior for Input Fields

To achieve the expected behavior of filling available space for fields:

• Try width: 100%: This sets the width to the remaining space within the container, similar to the behavior of other block-level elements.

If width: 100% Fails:

It may be due to the default size attribute, which defines the size of the input area. To override this, remove the size attribute or set it to an empty string (e.g., size="").

Example with width: 100%:

<code class="html"><form style="width: 200px; background: khaki">
  <input style="width: 100%" />
</form></code>

Partial Solution with Margins and Borders:

For a more precise solution, add negative margins and inset borders to the input field, as seen in this code:

<code class="html"><div style="padding: 30px; width: 200px; background: red">
  <form style="width: 200px; background: blue; padding: 3px">
    <input style="width: 100%; margin: -3px; border: 2px inset #eee" />
  </form>
</div></code>

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