Make a field fill its container

[Juan Asensio Sánchez]

Hi

I have this:

<div class="tab-content">
        <div id="general" class="tab-pane active">
                <div class="control-group">
                        <label class="control-label" for="siteName">Site 
name</label>
                        <div class="controls docs-input-sizes">
                                <input type="text" name="siteName" value="Site 
name" id="siteName" />
                                <p class="help-block">Use the same 
<code>.span*</code> classes
from the grid system for input sizes.</p>
                        </div>
                </div>
        </div>
</div>

How can I make the text field fills with its width the parent
container, i.e. occupy all the width of the page?

Regards and thanks in advance.