Elgg's css are view files. You have to extend the core css with your's. See http://docs.elgg.org/wiki/Getting_Started_With_Development 

Thanks for the quick reply - looking at the docs now

Thanks

Good day

I have done the following but still no luck:

I deactivated the Use system cache

In file > /views/default/css/elements/core.php

At the bottom I added the following clas "top"

.top {
background:#000000;


}

But My custom html has not changed.

How do I get access to the css file that are located> /cache/css/default/elgg.1356710142.css

Thank you

You shouldn't edit core css file. Copy blog plugin, the css view is located at blog/views/default/blog/css and then the core elgg css is extended with:

elgg_extend_view('css/elgg', 'blog/css');

Good day

Sorry but I dont see the following folder blog/views.... ?

Where in the core.php must I add this code?

elgg_extend_view('css/elgg', 'blog/css');

Here is an images of the class I want to edit?

Thank you