It looks like they're maybe not marketing it heavily right now, but in the web app under settings there's an upgrade to pro option - its $4.99 a month or $49 a

It looks like they're maybe not marketing it heavily right now, but in the web app under settings there's an upgrade to pro option - its $4.99 a month or $49 a year and gets you dropbox sync, themes, extra fonts and unlimited lists / items.