If you have an html file, and in that html file you link to styles.css which covers all the styling of the page. Then inside of styles.css you have something like @import url('../css/fonts.css'). Fonts.css is just a couple dozen font-face declarations. Basically covering all of your bases.
If styles.css only uses one or two of those fonts, will there be a performance hit when the browser tries to download all of the unused fonts in fonts.css, or will it only download the ones it needs as it comes up?
Similarly, what happens if fonts.css was linked inside of the HTML file?