Cursor becomes invisible

[L1szt]

I'm using the base16-nord theme but after having installed it my cursor becomes "invisible" or rather has the same colour as my back -and foreground. I tried several things like

highlight nCursor guibg=#51afef
set guicursor=n-v-c-i:block-nCursor
set guicursor+=i:ver25-nCursor
set guicursor+=o:hor50-nCursor

or

set guicursor=n-v-c:block,i-ci-ve:ver25,r-cr-o:hor20

but they didn't change anything.