Fixed position on the page

[Suriname]

When I (or a user by accident) scrolls when the Slimbox is activated,
the image scroll with the page.
I tried modifying the position in css to "fixed", but this places the
div out of the browser window.
Can this be an option in the base of the code with a config-setting,
or can someone help me out here ?
I don't have any JS experience (only HTML/CSS/PHP). I'm guessing the
Slimbox position is generated from the JS each time it is clicked, so
it is at a different place each time it's opened.

Regards,