How to exit desktop app?

Sounds like a dumb question...but earlier, when I brought up the popup for the desktop app, from the taskbar, my little avatar which I click to use to close the app was hidden off the side of my screen. For some reason the popup wasn't fully visible onscreen, and I couldn't find a way to fix it. Trying to end Dropbox from the task manager just borked it up and wouldn't exit it; I had to restart the computer. It's working now, the menu is displaying properly, but that was annoying. Are there no alternative ways to quit the app?

How do you properly exit the app when you can't access the avatar you use to bring up the "Quit" menu?