The class name is menu-button
Change :nth-child(n) to suit your menu structure.
Add code according to the number of your navigation menus.
/*Custom menu 1*/
#page-root:has(nav ul > li:nth-child(1) > .menu-item.active) .menu-button button:nth-child(1) {
background-color: var(--gv-w10A);
}
/*Custom menu 2*/
#page-root:has(nav ul > li:nth-child(2) > .menu-item.active) .menu-button button:nth-child(2) {
background-color: var(--gv-w10A);
}