Remove class nuxt-link-exact-active or giving style css on it

Question

i want to give class active in each href based on current link. but now i have problem about remove class nuxt-link-exact-active or giving style on it,

i my current template already has style

.mainNav .nav-item.active .nav-link 

so all i need to do

1. remove class nuxt-link-exact-active
2. giving style nuxt-link-exact-active

but i did number 2 but still not working

this is my demo https://codesandbox.io/s/m3rpmrk0xj