Cannot modify Comment form Width

I have a pretty frustrating problem with my comments form. I cannot get the “Comment” textarea to the correct width. I can change the width of the “Name,” “Email,” and “Website” textareas with no problem, but not the “Comment.” At this point I have been attempting this in the Master.css without success. My only thought now is that something is overriding it. FYI, I am using the Vigilance theme, which I modified to make approximately 100px skinnier.

Here is an example of my issue, scroll down to the bottom for the comment form…

http://www.vincentmcneill.com/2010/02/28/america-no-trespassing/

/*Form
—————————————*/

form#commentform { margin-bottom: 20px; }
#respond { font-size: 1.5em; }
h4#postcomment {
margin: 20px 0;
padding: 0 0 5px 0;
font-size: 1.2em;
color: #555;
border-bottom: 1px solid #eee;
}
form#commentform label.comment-field {
display: block;
margin: 10px 0 5px 0;
}
input.text-input, form#commentform textarea {
width: 500px;
padding: 7px;
background: #f8f8f8;
font-family: inherit;
font-size: 0.9em;
border: 1px solid #E6E6E6;
}
input#author, input#email, input#url { width: 350px; }
form#commentform input:focus, form#commentform textarea:focus {
background: #fff;
}
form#commentform input#submit {
padding: 5px;
width: 150px;
}
form#commentform p.guidelines {
margin: 10px 0;
font-size: .8em;
color: #777;
}
p.subscribe-to-comments, p.comments-rss {
margin: 0 0 10px 0;
font-size: .9em;
}
p.comments-rss a {
padding: 0 0 0 19px;
background: url(../images/feed-icon.png) no-repeat 0 .15em;
}

Thanks for you help. Let me know any info I can provide that might help track down this issue.