Everyone's answer is correct, you can always find where the file is and then open it that way. You do have another option though...
If you use firefox as your browser you can download the Web Developer extension which will provide you several resources as a tool bar. One of the options of this tool bar will allow you to click and View the CSS or disable it or whatever you like. I use this extension all the time.
The CSS file is located in the file manager of the web hosting site. If you are the webmaster and have user name and password to get into the control panel and inside the file manager you can then see the CSS file.
between the 96e89a298ea9f469b9ae458d6afae9f96e89a298ea9f469b9ae458d6afae9f tags upload: replace URL_TO_YOUR_CSS_FILE with the particularly url on your css report. you may also change the media characteristic to question particular show screen sizes etc (if you're planning on coding a cellular webapp).
Sometimes, the file is usually in the root directory, and is commonly called styles
so if you went to http://www.website.com/Styles.css you might get it or try some other variations (e.g. www.website.com/website.css or websitestyles.css