docs: update site style

Author: tangjinzhou

site/src/theme/static/icons.less

@@ -83,7 +83,7 @@ ul.anticons-list {
 .copied-code {
   padding: 2px 4px 2px;
   font-size: 12px;
-  background: #f5f5f5;
+  background: transparent;
   border-radius: 2px;
 }