How to change navigation links size on smaller screen?

To change the navigation links size on smaller screen, you can use this CSS code to Custom CSS box.

@media screen and (max-width:1200px) and (min-width:995px) {
    div.header-nav-item>a {
        font-size: 12px !important;
    }
    div.header-nav-item {
        margin-left: 5px !important;
        margin-right: 5px !important;
    }
}

Note: this code will run on screen size 995px to 1200px. You can adjust these numbers