::after class within JSX

Hi guys, i’m creating some sort of LineMenu where my <NavLinks> are displayed. I used NavLink in order to easly check wich one is currently active and now i want to give underline, but i cant go with borderBottom or underline because i have some lines by design that i need to follow, so i have to go with ::after

Im using MaterialsUI, and within NavLink im using style so i can pass an object.

const activeLink = { color: “blue”, textDecoration: “none”, marginRight: “50px” lineHeight: “21px”, “& ::after”: { content: “”, position: ‘absolute’ . . .}

And i did care about parents relative positioning etc. I just think that its about syntax