Fix no-highlight code blocks for dark themes

Former-commit-id: d5e8fcb3

app/assets/stylesheets/generic/typography.scss

@@ -90,9 +90,6 @@ a:focus {
   font-size: 14px;
   line-height: 1.6;
-  .white .highlight pre {
-    background: #f5f5f5;
-  }
   ul {
     padding: 0;
     margin: 0 0 9px 25px !important;

app/assets/stylesheets/highlight/dark.scss

@@ -9,6 +9,10 @@
     border-left: 1px solid #444;
   }
+  .no-highlight {
+    color: #DDD;
+  }
+
   .line-numbers a {
     color: #666;
   }

app/assets/stylesheets/highlight/monokai.scss

@@ -9,6 +9,10 @@
     background: #558;
   }
+  .no-highlight {
+    color: #DDD;
+  }
+
   .line-numbers a {
     color: #666;
   }

app/assets/stylesheets/highlight/solarized_dark.scss

@@ -9,6 +9,10 @@
     background: #000;
   }
+  .no-highlight {
+    color: #DDD;
+  }
+
   pre {
     background-color: #002B36;
     color: #eee;