Of course you can do any style change you want. But you need to do those style changes through this CSS file: /plugins/system/flexibleZoomEffect/media/css/flexibleZoomEffect.css
Since style changes are 100% custom modifications; we don't provide step-by-step instructions for custom coding modifications. Because there is no limit for them. We provide free support only in case of any bug or failure.
If you use "Firebug" or any "Inspect Element" tool (Chrome's build-in inspect element tool is also great) then you can do those CSS styles changes without any hassle in couple minutes