CSS classes added to typography.css should show up in this file. However, it's a little finicky sometimes. I've found that it works best if you make it a global CSS class (so, just a style item with a dot in front of it.)
Like..
.headline {font-size: 18px;}
In typography.css
should show up in the Styles menu (you may need to clear your cache or even restart your browser.)
Like..
.headline {font-size: 18px;}
In typography.css
should show up in the Styles menu (you may need to clear your cache or even restart your browser.)