It may be a block loading up the CSS. However, in any case it's important that CSS is written so it can all be loaded at once without any adverse reaction (other than performance).

To target styles to a specific page you can use the page_running_<pagename> CSS class we automatically inserted into the DOM tree.

E.g.
.page_running_downloads p { color: red; }

would make all paragraphs red but only on the download page.

Yeah I know how to do that, wasn't sure if this was intentional. Cheers