Update core CSS files

src/epub/css/core.css

@@ -92,6 +92,12 @@ strong{
 	font-weight: normal;
 }
 
+i > i,
+em > i,
+i > em{
+	font-style: normal;
+}
+
 header{
 	break-after: avoid;
 	break-inside: avoid;

src/epub/css/se.css

@@ -1,6 +1,11 @@
 @charset "utf-8";
 @namespace epub "http://www.idpf.org/2007/ops";
 
+/* This may appear in the colophon */
+abbr.era{
+	font-variant: all-small-caps;
+}
+
 section[epub|type~="titlepage"] img{
 	display: block;
 	width: 100%;