remove background color styles for pre and code

Author: euclio

github-markdown.css

@@ -603,7 +603,6 @@
   padding: 0.2em 0.4em;
   margin: 0;
   font-size: 85%;
-  background-color: rgba(27,31,35,0.05);
   border-radius: 3px;
 }
 
@@ -617,7 +616,6 @@
   font-size: 100%;
   word-break: normal;
   white-space: pre;
-  background: transparent;
   border: 0;
 }
 
@@ -636,7 +634,6 @@
   overflow: auto;
   font-size: 85%;
   line-height: 1.45;
-  background-color: #f6f8fa;
   border-radius: 3px;
 }
 
@@ -648,7 +645,6 @@
   overflow: visible;
   line-height: inherit;
   word-wrap: normal;
-  background-color: transparent;
   border: 0;
 }