[Twenty Eleven] How to change text colour in the search box

Hi, I’m using a child theme based on twentyeleven and I’m trying to change the colour of the text “search” that appears in the search box before clicking on it. At the moment is greish and not very visible and I would like to change it to white. See here

I’ve tried copying all the code from the main stylesheet and change the colour here but nothing happened. Here is the code that I’ve copied from the main stylesheet into the child stylesheet:

[CSS code moderated – a link to your site is enough to access the styles]