Create a file called functions.php in the child theme.
Add <?php right at the top of the file and then paste this code in.
http://pastebin.com/yWFD4yBa

Add this css to the styles.css

#searchform{
margin:7px;
}

#searchform-item input[type="text"] {
    width: auto;
}

This will only work if a custom menu has been created.

Ulrich