A similar hook as wp_head for the admin area

I’m adding a node to the toolbar and wish to tweak the css a bit.
I don’t have any external CSS files and I’m echoing the CSS using the wp_head action hook. Is there a similar action hook that I can use to echo the CSS everywhere? Both front-end and admin area?

The alternative to wp_head action in admin area is admin_head. But, if your CSS depends on another stylesheet, you should use wp_add_inline_style() function hooked to admin_enqueue_scripts action.