fixed bg for dark file preview

app/assets/stylesheets/highlight.black.css.scss

@@ -11,7 +11,7 @@
   .cm { color: #888888 } /* Comment.Multiline */
   .cp { color: #cc0000; font-weight: bold } /* Comment.Preproc */
   .c1 { color: #888888 } /* Comment.Single */
-  .cs { color: #cc0000; font-weight: bold; background-color: #fff0f0 } /* Comment.Special */
+  .cs { color: #cc0000; font-weight: bold; background-color: auto } /* Comment.Special */
   .gd { color: #000000; background-color: #ffdddd } /* Generic.Deleted */
   .ge { font-style: italic } /* Generic.Emph */
   .gr { color: #aa0000 } /* Generic.Error */
@@ -30,7 +30,7 @@
   .highlight .kt{color:#458;font-weight:bold;} /* Keyword.Type */
   .m { color: #0000DD; font-weight: bold } /* Literal.Number */
   .p { color: #eee;  }
-  .s { color: #dd2200; background-color: #fff0f0 } /* Literal.String */
+  .s { color: #dd2200; background-color: auto } /* Literal.String */
   .highlight .na{color:#008080;} /* Name.Attribute */
   .highlight .nb{color:#0086B3;} /* Name.Builtin */
   .highlight .nc{color:#4d3;font-weight:bold;} /* Name.Class */
@@ -48,9 +48,9 @@
   .mh { color: #0000DD; font-weight: bold } /* Literal.Number.Hex */
   .highlight .mi {color:#099;} /* Literal.Number.Integer */
   .mo { color: #0000DD; font-weight: bold } /* Literal.Number.Oct */
-  .sb { color: #dd2200; background-color: #fff0f0 } /* Literal.String.Backtick */
+  .sb { color: #dd2200; background-color: auto } /* Literal.String.Backtick */
   .highlight .sc{color:#d14;} /* Literal.String.Char */
-  .sd { color: #dd2200; background-color: #fff0f0 } /* Literal.String.Doc */
+  .sd { color: #dd2200; background-color: auto } /* Literal.String.Doc */
   .highlight .s2{color:orange;} /* Literal.String.Double */
   .highlight .se{color:orange;} /* Literal.String.Escape */
   .highlight .sh{color:orange;} /* Literal.String.Heredoc */