Change text size on portrait iPad

Hi. I need to add a @media screen code to reduce the font size when menu is displayed on portrait iPad eg, 768px wide. I have tried various versions of the link I find when inspecting the code, but none are working. What is the class I need to put in the css below?

@media only screen and (max-width: 800px) {
???????????? {
font-size: 12px;
}
}

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