Being new to elgg finding the css to modify was a chore in itself >< (no hints, keep looking)

What I will tell you however is that today I learnt not every plugin needs its own css file - simplistic but awesomely powerful!

Check out what I found on the Docs site:

View overloading Plugins can have a view hierarchy, any file that exists here will replace any files in the existing core view hierarchy... so for example, if my plugin has a file:

/mod/myplugin/views/default/page_elements/spotlight.php

it will replace:

/views/default/page_elements/spotlight.php

But crucially, only when the plugin is active.

This gives you total control over the way elgg looks and behaves. It gives you the option to either slightly modify or totally replace existing views.