How do I define my own font?

In the table object there is an option of "Define your own font" in the font family, how do I use this option?  I want to use a google font.

I have tried with this format, but isn't working:

@font-face {

    font-family: 'Montserrat Alternates', sans-serif;

    src: url('https://fonts.googleapis.com/css2?family=Montserrat+Alternates:wght@100&display=swap');

}