How test css indicator overlapping with qunit and ember testing

One css element is overlapping the comment section, because it has a width of 100% (and the solution to that is to remove the width). Therefore a part of the comment section could not be selected. Now I want to write some test to check this.

With JavaScript I created some elements and gave it styling. But how should I complete this test, in order words what is the best way to fail first and to succeed when the codes has been modified.