How do I change fonts in a Chrome OS app?

I have searched around the Internet to learn how to change the text font in a chrome OS app. The search results are for changing the font in the context of the OS user, not the app developer.

I tried using the normal CSS method of changing the font:

font-family: "Open Sans", Arial, serif;

The font family doesn't change from Arial or serif to Open Sans. Why? How can I do that?

Solution

Please import also below style

<style>
@import url('https://fonts.googleapis.com/css?family=Open+Sans:300,400,600,700,800&subset=cyrillic,cyrillic-ext,greek,greek-ext,latin-ext,vietnamese');
</style>