First pass at NNTP theming....

chrome/browser/resources/new_new_tab.css

 html {
   /* This is needed because of chrome://theme/css/new_tab.css */
   height: 100%;
 }
 
 body {
   margin: 0;
 }
 
 #main {
@@ skipping 333 matching lines @@
   height: 40px;
   color: hsl(213, 27%, 68%);
   width: 100%;
 }
 
 .list .title > div {
   color: rgb(6, 45, 117);
 }
 
 .section {
-  background: white;
+  background: rgba(255, 255, 255, 0.8);
   -webkit-border-radius: 4px;
   white-space: nowrap;
   text-overflow: ellipsis;
   border: 1px solid hsl(213, 65%, 92%);
   overflow: hidden;
   min-height: 151px; /* height of 5 items plus the header */
   vertical-align: top;
   margin: 0;
   margin-bottom: 10px;
 }
@@ skipping 336 matching lines @@
   }
 
   #t3, #t7 {
     left: 534px;
   }
 
   #t4, #t5, #t6, #t7 {
     top: 147px;
   }
 }