Hiding Menu From Specific Pages

I’m trying to hide the menu page completely from this page:

http://ultimate-templates.com/splash-page

I’m using Divi 3.0, and have tried – through online tutorials – to hide it using the following in my styles css sheet:

.page-id-27820 top-menu-nav {
display: none important;
}

That didn’t do anything, aside from making the menu look a little weird (and dropping the search magnifying glass down a bit), and I removed the code – the search button still looks weird.

if anyone could help me with how to remove the menu completely (and logo etc) from that one page, I’d be very much appreciative!

Created a simple image for you on how to get page id and menu attributes.
https://dl.dropboxusercontent.com/s/zibhieyo3s6a5bs/Mailbird_2017-01-27_00-57-39.png

You need to get the page_id, exactly as you did:

.page-id-27820 

and hide the menu, like so:

.page-id-27820 #top-menu-nav {
    display: none;
}

You forgot the # sign, which stand for html attribute id

id = #
class = .