I should explained where the files are located that need to be changed. The file you need to change is style.css and it is located in \Data\sites\1\skins\styleshout-brightsideoflife.
The csshandler.ashx doesn't actually exist in the skin folder. mojoPortal will grab requests for this file and process the CSS combining. If you put that path in your browser, all of the site's CSS will be shown.
When you are modifying any skin, make sure you have the values below set to false in your user.config.
<add key="CacheCssOnServer" value="false" />
<add key="CacheCssInBrowser" value="false" />