Using custom fonts for Newsletter, Buttons, et al.

Site URL: https://fightclubphilippines.org

I've applied a custom font to my headers and general text--no problem, but I don't know how to do it for the Newsletter, Buttons, other areas. Is there any easy way to do this? Thanks for the help.

Add to Design > Custom CSS

div#block-05572f6ffad31d43a714 * {
    font-family: Montserrat !important;
}