it is in _css/css.css 

I learned a cool trick today in google chrome. place the cursor on the item you want to find then right click and choose inspect element. That will show you exactly where it is :)

most/all browsers have a similar feature.. you can install 'firebug'  in firefox for the same 'inspect element' menu option. ;)

@woodpecker As Trajan says, just go to "Site Administration" and uncheck "Use simple cache".

I take less clicks. Just on/off in  a second :)

@brandon: The 'overwriting' is done based on the plugin list in your Tools Administration. Stick your theme right at the bottom of the list and see if things change.

If it still isn't working after what you said you tried, then it may well be a problem with your CSS syntax.

Post up an example of the code you are trying to use in your theme's CSS file for us to help further.

mod/uservalidationbyemail

Use Mass Mailout plugin.

But make sure your hosting-provider allows such scripts ;)

@ Brandon : http://community.elgg.org/pg/plugins/webgalli/read/485322/mass-mailout-plugin-for-elgg-send-messages-to-all-users