Change sub menu font size in mobile

Hi, I'm sorry if this has been asked before, but I searched for it and I couldn't find any answer.

If there is any way to change the size of the sub-menu fonts in mobile? I saw that this code had been suggested to a similar problem:

.main-navigation .main-nav ul ul li a {
font-size: 16px;
}

But this only solved the problem in desktop, not in mobile.

Thanks in advance!