Form width

I am trying to change the form width of the MailChimp newsletter signup form in the right sidebar of I added the following to the text widget:

form {

It seems to have no effect. What am I missing?

/* Add your own MailChimp form style overrides in your site stylesheet or in this style block. We recommend moving this block and the preceding CSS link to the HEAD of your HTML file. */

Hi Paul, if you inspect the code with a tool like Firebug you can see this message. Try either doing what they recommend (adding to the HEAD or adding the !important tag to your custom width. You are essentially trying to override their default width (not sure how it is being generated), so your instruction needs to come first or be bumped up in importance by use of the !important tag.