By default mojo caches the css and html for the site to improve speed. If you are modifying skins, I suggest you set the following in your user.config file and then "touch" the web.config (open it, add a space, save it). After doing this, reset your browser's cache.
<add key="CacheCssOnServer" value="false" />
<add key="CacheCssInBrowser" value="false" />
If you just want to see your new css file added, you can just touch the web.config and clear your browser cache.
You will not see a link to the scrollstyle.css file in the header because the css files listed in the style.config are combined using mojo's CSS Handler. You will instead see a single link to the csshandler.ashx file.
Hope this helps,