Updated colors to fix issue

public/sass/_variables.dark.scss

@@ -102,7 +102,9 @@ $tight-form-func-bg: 		    #333;
 $tight-form-func-highlight-bg:  #444;
 
 $modal-background: $black;
-$code-tag-bg: #444;
+$code-tag-bg:      $dark-5;
+$code-tag-border:  lighten($code-tag-bg, 2%);
+
 
 // Lists
 $grafanaListBackground:  	  $dark-3;

public/sass/_variables.light.scss

@@ -109,7 +109,8 @@ $tight-form-func-bg:            $gray-5;
 $tight-form-func-highlight-bg:  $gray-6;
 
 $modal-background: $body-bg;
-$code-tag-bg:      $dark-5;
+$code-tag-bg:      $gray-6;
+$code-tag-border:  darken($code-tag-bg, 3%);
 
 // Lists
 $grafanaListBackground:    	   $gray-6;

public/sass/base/_code.scss

@@ -10,7 +10,7 @@ pre {
   font-size: $font-size-base - 2;
   background-color: $code-tag-bg;
   color: $text-color;
-  border: 1px solid darken($code-tag-bg, 15%);
+  border: 1px solid $code-tag-border;
   padding: 10px;
   border-radius: 4px;
 }