Change dark theme from black to dark gray and add a black theme

cps/static/css/epub_themes.css

@@ -4,11 +4,16 @@
 }
 
 .darkTheme {
-	background: #000;
+	background: #202124;
 	color: #fff
 }
 
 .sepiaTheme {
 	background: #ece1ca;
 	color: #000;
+}
+
+.blackTheme {
+	background: #000;
+	color: #fff
 }

cps/static/css/main.css

@@ -578,7 +578,7 @@ input:-moz-placeholder { color: #454545; }
 }
 
 .md-content .themes button.darkTheme {
-  background-color: black;
+  background-color: #202124;
   color: white;
 }
 
@@ -592,6 +592,11 @@ input:-moz-placeholder { color: #454545; }
   color: black;
 }
 
+.md-content .themes button.blackTheme {
+  background-color: black;
+  color: white;
+}
+
 /* Effect 1: Fade in and scale up */
 .md-effect-1 .md-content {
   -webkit-transform: scale(0.7);