Hello Ed,
I am really sorry for the delay of this reply as it is a weekend for us here.
You should put it in your templates css file and follow below location :
JoomlaFolder/templates/yoo_lava/styles/sdrain/css/theme.css
Please let us know if you need further assistance. If yes, could you please provide me with a temporary access to your website (as admin) and an FTP access so I can add the css code in your templates file? Hope this help.