Private equity firm Leonard Green & Partners announced plans Thursday to acquire The Shade Store, a customized window treatment company.

The deal was valued at about $325 million, sources familiar with the situation told CNBC, which first reported the deal. The sources requested anonymity because the terms are confidential.

The acquisition highlights the opportunity private equity firms continue to see in niche retailers that marry online and offline businesses, despite the challenges the retail industry has seen over the past several years. For Leonard Green, it marks a shift in strategy away from its larger retail bets in recent years, like J.Crew, David's Bridal and BJ's Wholesale Club. Many private equity firms with retail expertise have shifted their focus away from large retailers with expansive real estate, as they look instead toward smaller brands with more runway.

The Shade Store sells its window products online and in 60 showrooms across the country.

It started in 2006 as a website that offered customized window treatments. Two years later, it launched showrooms in New York and San Francisco to promote its products and allow customers see them in person.

Many online retailers, including Bonobos and Warby Parker, have opened brick-and-mortar stores in recent years, because the market for digital shopping has become flooded and the cost to compete for online eyeballs has risen.

The Shade Store sold to private equity firm Great Hill Partners in 2013. Great Hill's investments have included online brands like home furnishings company Wayfair and vitamin and supplement seller Vitacost.

Under Great Hill, the drapery retailer built out showrooms across the East Coast and on the West Coast, the Northwest and states including Arizona, Ohio and Illinois. It often places those showrooms in clusters, to appeal to shoppers whose interest may be piqued by driving past one, but who may not be quite ready to buy drapes.

Its shoppers spend on average $2,800 in showrooms and $1,000 online. Its products includes shades, drapery and blinds, which it customizes with designer materials, trims and decorative borders. It offers installation and free shipping.

Under Leonard Green's ownership, the company expects to continue to expand its footprint across the U.S. The customized window treatment business remains highly fragmented, dominated by mom-and-pop offerings.

It may also go further into private label, having already signed a partnership with RH, the home furnishings company formerly known as Restoration Hardware. It will also look to increase its sales to hotel chains, restaurants, gyms or other businesses.