Customized divider weirdness

The first dark divider looks right in my project using scss, but wrong in the codepen. The second dark divider looks exactly the same in my project, completely wrong. Why is there a difference between the two?

Shouldn’t “item-divider-dark” and “item-divider-{{theme}}” evaluate to the same thing when $scope.theme is ‘dark’?

apparently it needed ng-class="‘item-divider-’ + theme" instead of class=…