In overall_header.html, an EVENT should be available after the STYLESHEETS tag.
This would allow style tags to be used after the included CSS files that can over-write styling from the linked CSS files if needed. It can also allow stuff to truly be inserted immediately before the closing head tag.
But we still need the EVENT before STYLESHEETS so extensions can use INCLUDECSS.
Perhaps have a new prepend event and some re-arranging: