The Grade Me block implements the class '.toggle' that is generic and not specific to the block. The Collapsed Topics course format also uses that class name but with a specific selector pertaining to itself only. Because of this there is a right arrow within the toggle. Due to the nature of the implemented selector there is no way for Collapsed Topics to alter its CSS in such a way that it could override the Grade Me CSS and solve the problem.

Examples of which can be seen here: https://moodle.org/mod/forum/discuss.php?d=268539 and here: https://moodle.org/mod/forum/discuss.php?d=315235#p1262776.

The offending CSS is:

.jsenabled .toggle {

background: transparent url('/theme/image.php/magazine/block_grade_me/1409650493/closed') no-repeat 50% 50% !important;

}

It is customary for plugins to have their CSS separate and written in such a way to avoid conflicts like this. Please would you be so kind as to change yours accordingly. For example using '.block_grade_me' as a prefix in the selector.