Changing the default's lightdm greeter

first of all, sorry if this a kind of a noobs question, i’ve been trying to find out about it myself but i found nothing until yet, so i decided to ask it here.

i’m trying to use lightdm-webkit2-greeter instead of the default one, but i’ve no luck in it. i’ve tried a couple of methods like this one Customising lightdm but it still won’t work at all for me, the config is already at it’s peak but it won’t take any effect at all.

i’ve tried to search for the lightdm.conf and i’ve found it in the ubuntu-mate directory but it still won’t take effect.

fyi, this is why i want to try using webkit2 https://github.com/artur9010/lightdm-webkit-material and sorry for my bad english.