[Plugin: Contact Form 7] Make text field responsive CSS

I am placing contact form 7 in my side to use it is for newsletter subscription. I am tyring to style the plug-i so that the text feild automatically resizes to fit the the sidebar perfectly. I would like to do this through CSS. I have come up with the following code, but it does not work properly. Can someone help me?

.wpcf7-form-control.wpcf7-text {
border: 1px solid #000000;
background-color:#ffffff;
width:90% auto !important;
}

I was hoping this code would do the trick, but it does not.

http://wordpress.org/extend/plugins/contact-form-7/