Add Google Fonts in Layerslider

Hey

I tried to add Google Fonts to layerslider by adding a new google font on the layerslider menu (in wordpress). In my case its roboto with the options 100, 500, and regular. But when I add this code into my custom CSS under layers → Style, there is no difference between roboto:100 and roboto:500 and roboto:regular:

font-family: 'roboto', 100;
or
font-family: 'roboto', 500;
or
font-family: 'roboto', regular;
But there is no difference between the codes, but the font family itself (roboto) works (that means, I can see that the font family changes to roboto). How do I have to type in the “100” or “500” or “regular” or options like this?