Different Font Size Submenu

Hi there,

Thanks for creating this amazing plugin! I’m currently using the left menu and would like to use a different font size for my submenu items (the ones that appear when I toggle open a regular menu item). Could you please help me out? I tried adding the following CSS but it didn’t work.

@media only screen and (max-width: 600px) {
.site-navigation .sub-menu {
font-size: 20px!important;
}
}

Many thanks!