As Quora’s product design manager, Cox is the whiz behind the site’s intuitive user interface, which compels people to keep coming back to seek or share information. Visually, Quora isn’t flashy or particularly cool-looking — and that’s the point, says Cox, 31. “The best design is design you don’t notice.”

Quora was founded in summer 2009 by a couple of star engineers from Facebook, Charlie Cheever and Adam D’Angelo. Cox was their first employee. Their aim: to coax users to share their knowledge and expertise to create an ever-deepening (and searchable) database of answers.

There are few hints of the founders’ lofty ambitions in Cox’s utilitarian design, though. Members post and answer questions. They can vote an answer up or down so the highest-quality answers migrate to the top.

Users appear to agree: 200,000 members return to the service each month. But if Quora, which has raised $11 million in funding, is going to succeed, it must win attention beyond tech circles, and that’s why design matters. The site must be so simple that people who consider Facebook high tech can figure out how to use it.

Good thing, then, that Cox honed her craft at, yes, Facebook. After getting a computer science degree from Augustana College in Rock Island, Ill., she spent several years working at the University of Iowa, tinkering on design projects in her spare time. A Facebook designer stumbled across her work on the Net and tried to recruit her. After flying out to meet Mark Zuckerberg in 2006, she passed on the offer. (“I thought Facebook was a dating site for college kids,” she says, glancing at her signature teal Nikes.) But when Facebook came calling again a year later, Cox signed on. She worked there two years, rising to become the interim director of design and user experience, just as the social network was going mainstream.

Now she helps manage a team of more than 20 in Quora’s Palo Alto offices, next door to the old Facebook headquarters. The culture may seem laid-back on the surface, but like the Quora site itself, there’s actually a real sense of order and focus. And given Cox’s worldview, that’s probably by design.