Have looked at your sit, in particular at the head section. There is only one call to for css to be loaded and that is
<link href=/media/gantry5/assets/css/font-awesome.min.css rel=stylesheet />
but there is a huge amount of explicit css in the head section.
This is down to some load time optimisation process, maybe in your template perhaps. But I have never tried that method. Maybe what ever is doing the 'optimisation does not know about css associated with other components.
I have made the head section into a separate html file and will send you separately.
This is not a jD thing but probably a template issue.
Perhaps you could tell me what templates or optimising addons you are using.