lisp/ox-html.el: Enhance `org-html-style-default'

* lisp/ox-html.el (org-html-style-default): Enhance.

lisp/ox-html.el

@@ -280,8 +280,9 @@ property on the headline itself.")
   #postamble p, #preamble p { font-size: 90%; margin: .2em; }
   p.verse { margin-left: 3%; }
   pre {
-    border: 1px solid #ccc;
-    box-shadow: 3px 3px 3px #eee;
+    border: 1px solid #e6e6e6;
+    border-radius: 3px;
+    background-color: #f2f2f2;
     padding: 8pt;
     font-family: monospace;
     overflow: auto;
@@ -290,16 +291,15 @@ property on the headline itself.")
   pre.src {
     position: relative;
     overflow: auto;
-    padding-top: 1.2em;
   }
   pre.src:before {
     display: none;
     position: absolute;
-    background-color: white;
-    top: -10px;
-    right: 10px;
+    top: -8px;
+    right: 12px;
     padding: 3px;
-    border: 1px solid black;
+    color: #555;
+    background-color: #f2f2f299;
   }
   pre.src:hover:before { display: inline; margin-top: 14px;}
   /* Languages per Org manual */