[1] Open Publication Structure (OPS) 2.0.1 v1.0 (9/7/2015, 7:50:12 PM 版) <http://www.idpf.org/epub/20/spec/OPS_2.0_latest.htm#Section1.3.5>
The style sheet MIME type text/x-oeb1-css has been deprecated in favor of text/css.
Google search: text/x-oeb1-css