To craft the looks of Paul Thomas Anderson’s “Licorice Pizza,” costume designer and frequent collaborator Mark Bridges turned to references including high school yearbooks and store catalogs that showed how middle-class residents of the San Fernando Valley might have looked in 1973.

“The yearbooks would verify we were on the right track and were incredibly valuable. I’m kind of a method costume designer,” Bridges jokes of his approach, which also had him leafing through offerings from Sears and Montgomery Ward.

Alana Haim plays Alana, a 25- year-old who still lives with her parents and sisters and embodies the period with her extremely 1973 white Peter Pan collars and halter tops. Bridges felt the character would borrow clothes from her two sisters, and eagle-eyed viewers will notice a scene where one of them wears an outfit that is later worn by Alana.

With Cooper Hoffman’s Gary, a 15-year-old going on 30, the idea was that the character is a savvy high schooler who’s also an actor who goes to auditions and meetings. Collared shirts and vertical stripes were flattering and suited him. But Gary straddles a fine line where he’s still a teenager. “He dresses more mature than his peers, and you can tell who’s the boss, but he also runs around in sneakers and trousers, not always jeans,” Bridges says. “The color palette at that time was a rollicking good time. It was quite a colorful period, grounded with navy and brown,” he adds.

While Bridges has worked on ’70s-era clothing in films such as “Blow” and “Inherent Vice,” he hadn’t focused on that specific year.

To emphasize the spirit of the time, for a sequence when Alana and Gary fly to New York to take in a show, Bridges designed the stewardess outfits in a double-knit fabric in gold. “No other time except 1973 could you have put stewardesses in gold,” he says. “That gold is more buoyant than, say, a navy stewardess. It was about constantly looking for ways to emphasize the vibe and the period.”