Fix "run" button position in error index

Author: GuillaumeGomez

src/doc/rust.css

@@ -332,6 +332,7 @@ table th {
 
 /* Code snippets */
 
+.example-wrap { position: relative; }
 pre.rust { position: relative; }
 a.test-arrow {
 	background-color: rgba(78, 139, 202, 0.2);

src/librustdoc/html/static/rustdoc.css

@@ -347,10 +347,10 @@ nav.sub {
 .rustdoc:not(.source) .example-wrap {
 	display: inline-flex;
 	margin-bottom: 10px;
-	position: relative;
 }
 
 .example-wrap {
+	position: relative;
 	width: 100%;
 }