Make code in headers not giant

(cherry picked from commit 4a66260b2c)

docs/_css/react.scss

@@ -5,8 +5,8 @@
 
 @mixin code-typography {
   font-family: 'source-code-pro', Menlo, Consolas, 'Courier New', monospace;
-  font-size: 13px;
-  line-height: 20px;
+  font-size: 0.8em;
+  line-height: 1.5;
 }
 
 $skinnyContentWidth: 650px;
@@ -683,9 +683,11 @@ p code {
 }
 
 .highlight pre code {
+  /* Respect line-height defined in <code> styles above */
+  display: block;
+
   /* Cancel out styles for `li code` in case we have a <pre> within an <li>. */
   background: none;
-  font-size: inherit;
   padding: 0;
 }