http://tracker.moodle.org/secure/attachment/30510/EnrolPageFormalWhite.png

See MDL-36339. Something about the html structure on the course enrolment page isn't quite right.

From Marina:

The solution is to insert a line before https://github.com/moodle/moodle/blob/master/enrol/renderer.php#L93 :

$content .= html_writer::tag('div', '', array('class' => 'clearfix'));