detect if plugin activated

Hi,
We are you using a custom stylesheet for some of the elements in wpdm to better match our theme. I only want to load the stylesheet on sites in the network that have the plugin activated. I would typically use class_exists to accomplish this but I can’t find a class declaration in wpdm Is there one? If not, what do you recommend for testing whether the plugin is activated or not. function_exists?

Thanks,
Dan