Fixed missing color definion in docs CSS

config/nimdoc.cfg

@@ -93,6 +93,11 @@ doc.file = """<?xml version="1.0" encoding="utf-8" ?>
 <title>$title</title>
 <style type="text/css">
 
+body {
+  color: black;
+  background: white;
+}
+
 span.DecNumber {color: blue}
 span.BinNumber {color: blue}
 span.HexNumber {color: blue}