Currently the latest versions of all browsers understand all of CSS-1 and CSS-P. Only a few browsers support part of CSS-3 but most support at least part of CSS-2. Font selection was a part of CSS-1.
HTML is intended to identify what the various parts of your content are. Different browsers are free to choose how they display them unless you identify how you want it displayed. How you define the way that you want the page presented is to use CSS. Font selection is supported by all browsers that support fonts (eg. web readers don't and so ignore that part of the CSS).