Attempt to de-emphasise the source code section (#10215)

Fixes https://github.com/flutter/flutter/issues/9377

dev/docs/styles.html

diff --git a/dev/docs/styles.html b/dev/docs/styles.html
index 1a9662b..a111a6e 100644
--- a/dev/docs/styles.html
+++ b/dev/docs/styles.html
@@ -128,6 +128,10 @@
   li.inherited a {
     font-weight: 100;
   }
+
+  /* Attempt to de-emphasise the source code section */
+  section.summary.source-code { opacity: 0.3; }
+  section.summary.source-code:hover { opacity: 0.8; }
 </style>
 
 <!-- The following rules are from http://google.github.io/material-design-icons/ -->