remove relative and top positioning from docs sidenav at narrow layout

docs/assets/css/docs.css

@@ -760,10 +760,9 @@ form.bs-docs-example {
 
 .bs-docs-sidenav {
   width: 228px;
-  margin-top: 30px;
+  margin: 30px 0 20px;
   padding: 0;
   background-color: #fff;
-  margin-left: 0;
   -webkit-border-radius: 6px;
      -moz-border-radius: 6px;
           border-radius: 6px;
@@ -924,8 +923,9 @@ form.bs-docs-example {
     width: auto;
   }
   .bs-docs-sidenav.affix {
-    position: relative;
+    position: static;
     width: auto;
+    top: 0;
   }
 
   /* Unfloat the back to top link in footer */