Make it a fonts.scss.liquid and then add {{ ‘fonts.scss.css’ | asset_url | stylesheet_tag }} to theme.liquid

Example of formatting:

@font-face {
    font-family: 'BeausiteGrandThin';
    src: url('BeausiteGrandThin.eot');
    src: url('BeausiteGrandThin.eot') format('embedded-opentype'),
         url('BeausiteGrandThin.woff2') format('woff2'),
         url('BeausiteGrandThin.woff') format('woff'),
         url('BeausiteGrandThin.ttf') format('truetype'),
         url('BeausiteGrandThin.svg#BeausiteGrandThin') format('svg');
}