Change Submenu shadow

Hi, I've tried to change the shadow of the submenu like in this post https://generatepress.com/forums/topic/need-some-help-with-system-fonts/, but it doesn't make any changes. Is there anything wrong with the code?

.main-navigation ul ul {
    -webkit-box-shadow: 0 20px 29px 0 rgba(207,67,20,.5);
    box-shadow: 0 20px 29px 0 rgba(207,67,20,.5);
}