Don't use the custom-variables.scss for your classes, but use the main.scss. Make sure to put the class on a page and run the model, use the inspector to see if the class is used or ignored if a more specific class is more important.
it also depends how your using your class. for example if you'll add this class to primary button, chances are if shows the color of the primary button. Use the browser inspector the validate if additional classes are mandatory to make a more specific selection.