make markdown backgrounds match current theme (#637)

public/css/style.css

@@ -128,6 +128,10 @@ td {
 	color:#bbb;
 }
 
+.md-editor > textarea, .md-preview {
+    background: none !important;
+}
+
 /* Table style & fixes */
 .table > tbody > tr > th, .nowrap {
 	white-space: nowrap;