MDL-45231 theme_clean: default navbar to absolute when running behat

lib/behat/lib.php

@@ -170,6 +170,14 @@ function behat_clean_init_config() {
         }
     }
 
+    // Here we are forcing the navbar to be absolutely positioned in Chrome + Safari in order to
+    // avoid a driver bug whereby when the browser scrolls something into view it doesn't account
+    // for fixed positioned elements that end up obscuring the item thus leading to errors that
+    // could be avoided by scrolling an additional amount.
+    // This should be removed as soon as the drivers have been fixed.
+    $CFG->forced_plugin_settings['theme_clean'] = array(
+        'customcss' => 'body.safari .navbar-fixed-top {position: absolute;}'
+    );
 }
 
 /**