Well let's break it down, then.
(1) identify in what sequence the css files for your site get executed, and particularly when the Woo css is applied.
(2) ensure that any *additions* to your css configuration, which are aimed at repairing the float and other issues, are executed after Woo/last (even if you have to create another CSS file, to control this timing issue).
(3) enqueue this new css file in your theme's functions file. Using priority will help to ensure this file is last.
(4) using firefox/firebug or google chrome, identify the css changes needed for your site and introduce them into that last css file, as you test.
This method allows css overrides to be introduced without touching Woo code in any way, making them independent of future Woo upgrades.
And Bob's your uncle, Fanny's your aunt.