styles.css 'inactive' in editor

HI –
Changed the color of the boxes for the submission (Your message was sent successfully. Thanks.) in contact-form-7/includes/css/styles.css but the changes do not appear. I noticed that in the title in the editor, ‘inactive’ appears here: Editing contact-form-7/includes/css/styles.css (inactive)

How do I make this ‘active’ so my styles will appear? What code needs to be changed/updated and in which php page?

Many thanks.

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