“The Holiday” Costume Designer Says the 2006 Rom-Com’s Longevity Has Been the ‘Icing on the Cake’ (Exclusive)

Marlene Stewart created the timeless looks worn by stars Cameron Diaz, Kate Winslet and Jude Law in the movie

The Holiday has become a Christmas classic since its release 18 years ago.

For costume designer Marlene Stewart, the 2006 film's enduring popularity is simply another lovely layer to what was an unforgettable experience working alongside the "incredibly talented" cast, including Kate Winslet, Jude Law, Jack Black, Cameron Diaz and Eli Wallach.

"I think for me, to be able to work with these actors, that's one of the best joys of being a costume designer, is having a chance to work with incredibly talented, interesting and creative [people], a team like this. It was wonderful," she tells PEOPLE in an exclusive interview.

"So all around, it was just the icing on the cake that the movie has become sort of a holiday classic, and fortunately, I get to watch it over and over again every year," adds Stewart, noting that she loves seeing new audiences discover the Nancy Meyers-directed movie thanks to streaming.

Related: Cameron Diaz’s ‘Quiet Luxury’ Wardrobe in The Holiday Was Way Ahead of Its Time, Costumer Says (Exclusive)

"I cannot tell you, even the younger generation, the next generation, everybody says, 'Oh, The Holiday.' So I'm fortunate to have had the opportunity to work on it and I'm fortunate that it comes around every year and you get a chance to relive it," Stewart says. "It was so much fun to work on, and that fun translated."

"The idea was to have a look that was luxurious and fun," Stewart explains. "She's a professional woman here. At that time, even though it's 20 years ago, [it was about], 'What is it that women wear to work? What are the standards? How is that changing?' "

Never miss a story — sign up for PEOPLE's free daily newsletter to stay up-to-date on the best of what PEOPLE has to offer​​, from celebrity news to compelling human interest stories.

Related: 'The Holiday' Cast: Where Are They Now?

Stewart says Diaz, 52, and the movie's other stars had input into the looks worn by their characters. She says the collaborative dialogue between costume designer and actor is incredibly important on set.

"For many actresses, actors, they find the character with the clothing. 'Yeah, this is right. No, that's the edge. She wouldn't do this. Yes, this makes sense. This shows a certain part of her personality,' " Stewart explains. "There's so much feedback. It's so important. You want [the stars] to feel comfortable."