Adjusting width in Contact Form 7 plugin

So I’m having trouble adjusting the width of the drop-down menus in the Contact Form 7 plugin. I know this can be done in CSS, but how? I’ve tried it numerous ways in both the theme’s CSS stylesheet as well as the plugin’s, but with no luck. This is probably very simple. Help?

<p>Your Name (required)<br />
    [text* your-name] </p>

<p>Your Email (required)<br />
    [email* your-email] </p>

<p>Subject<br />
[select your-subject class:contactform "Please Make a Selection" "I have a general question/comment" "I would like to give site feedback" "I would like to advertise"]</p>

<p>Your Message<br />
    [textarea your-message] </p>

[captchac captcha-236 size:m border: #ffffff bg:#ffffff]<br />
Enter the text exactly as it appears (case sensitive).<br />
[captchar captcha-236]

<p>[submit "Send"]</p>