It's working since Moodle 2.7.1 up to 2.9.1+. We are using 2.8.7 with the Moodle default theme (Bootstrap).
1) Check version
2) Check you are using Bootstrap
3) Check you are using Weekly format in your courses
4) Check you set up the code in "Site administration/Appearance/Themes/Clean/Custom CSS"
ggarcia
^^