Hi Mike,
Thanks for your report!
I’ve added the issue to your previously reported Mini Cart task.
However, the problems are not so easy to solve because specificity always throws a wrench in our plans. A single class will always lose if it competes against several nested/chained classes, which cannot always be avoided. That is also the case here.
While your class is selected, add this custom CSS which targets the correct selector and has the same specificity as the default:
root .mini-cart-link i {
font-size: 50px;
}