You put that code in the CSS Inserts box in the theme options and replace the example id with your actual page id. The way I find the id is look at the page source and search for [body class] without the brackets. That should take you to a line that looks like the following.
<body class="page page-id-2204 page-template page-template-blog-php logged-in custom-background">
In this case you would use
as your selector
To find the selectors for the menus you want to hide I use Firebug.