How can I resize the div.itemToolbar?

This div is given a 650x100px but I need to shorten the height to 20px.
With Firebug / FireFox devTools, I cannot locate this setting.

This class is located in k2.css in default installations.
Some templates however use different css files.

If you are not using overrides you need to read this tutorial on how to override that css file:
getk2.org/documentation/tutorials/174-templating-with-k2-and-the-concepts-of-sub-templates