Boohoo, an online retailer for fast, affordable, fashion, has shifted to become mobile-first.

Boohoo’s business is dependent on customers frequently checking in for new product launches. Five hundred new products debut on the site each week, with about 100 pieces available for each. The Boohoo team then responds to what’s selling well by adding more inventory to popular products, and phasing out what doesn’t perform. Its merchandising strategy is reactive: Boohoo relies on Instagram and runway trends in order to take cues for its affordable styles. Lead time from product design to launch is about four to six weeks, according to Carol Kane, CEO of Boohoo.com.

Over the past four years, Boohoo has witnessed its customers, who are mostly younger millennials, shift from desktop to mobile. The company said that 70 percent of its total visits now happen on mobile, and while Boohoo doesn’t break out the percentage of sales that happen on mobile, Kane said that mobile checkout is “about even” with desktop — implying that sales are around 50 percent.

“We were designing our homepage and product pages for desktop, then changing the content for mobile,” said Kane, speaking at the WWD Digital Forum in New York City on Wednesday. “Now, it’s the other way around. I tell my creative team to design for mobile. Desktop is on the decline.”

With such reactive inventory, Boohoo is constantly updating its desktop and mobile homepages, product assortments and mobile apps to reflect what’s trending with consumers, changing displays up to a few times per day. The first place these shoppers, who are mostly young millennials, find the new product launches and trending styles is on mobile.

“We have a crowdsourced approach to inventory, with a reactive buying team. The influence of social media on what sells is unbelievable, and in the same way customers are finding that inspiration on their phones, they’re shopping there,” Kane told Glossy after her presentation.

Boohoo, which has a 70-person content team, uses user-generated content sourced from Instagram. The hashtag #MyBoohooStyle pulls in customer photos exclusively to the mobile app; products that are shown are then linked to in each post. The team then looks to what products customers are wearing and purchasing to determine trends.

“Instagram is our first point of contact,” said Natalie McGrath, Boohoo’s vp of marketing in the U.S., in a previous Digiday interview. “We use social channels to inform demand, and then pull that content directly into our app to drive conversion.”

Outside of user-generated content, Kane said that Boohoo’s content is the same on mobile as it is on desktop, but served differently. In the future, though, the company plans to use mobile-optimized tools like Facebook Messenger chatbots in order to reach the customer with information as they shop for products; for instance, if a customer is going to Coachella, Boohoo’s chatbot can display the forecast in Indio, California and suggest proper attire.

“When you’re online only, it’s all about customer journey,” said Kane. “We want her to say I’m looking for this dress in this size, and be able to find it easily.”