Merge pull request #3942 from bke-drewb/issue3941

app/assets/stylesheets/highlight/dark.scss

 .black .highlight {
+
+  background-color: #333;
+
   pre {
     background-color: #333;
     color: #eee;

app/assets/stylesheets/highlight/monokai.scss

@@ -8,6 +8,9 @@ $monokai-dark: #3b3a32;
 $monokai-purple: #ae81ff;
 
 .monokai .highlight {
+
+  background-color: #272822;
+
   pre {
     background-color: #272822;
     color: $monokai-fg;

app/assets/stylesheets/highlight/solarized_dark.scss

 .solarized-dark .highlight {
+  
+  background-color: #002B36;
+  
   pre {
     background-color: #002B36;
     color: #eee;

app/assets/stylesheets/highlight/white.scss

 .white .highlight {
+  
+  background-color: #fff;
+  
   pre {
     background-color: #fff;
     color: #333;