Her memories of recording “Rockin’ Around the Christmas Tree” are a little hazy. She remembers the producer placing decorations around the studio and blasting the air conditioner on a warm Nashville day to create a holiday spirit. The musicians, she recalls, nailed it in a couple of takes.

That’s about it. After all, Brenda Lee was 13 years old at the time — and it was 66 years ago, in 1958.

Somewhat implausibly, her celebration of a “Christmas party hop” is more popular today than ever before. It’s an unusual trajectory, even accounting for the fact that music listeners during the holiday season tend to embrace songs they’ve known for years.

“Rockin’” eclipsed Mariah Carey’s perennial favorite “All I Want for Christmas is You” last December to top the Billboard music chart and make Lee, at age 78, the oldest woman to achieve that feat. A week later, following a birthday, she beat her own mark. Kendrick Lamar likely stands in her way of doing it again this year.

Another record: Sixty-five years represented the longest interval between a record being released and making it to No. 1.

“It is a good song,” Lee told The Associated Press. “It’s a song that anybody can sing. You can join in, you can sing it, everyone is happy. I sure am glad that I have it. I never thought in my life that a Christmas song would be my legacy. But I’ll take it.”

It’s a phenomenon that music journalist Holly Gleason noticed recently while stopping for coffee in Florida. The song came over the loudspeaker and the room — parents, kids, hipsters — erupted in singing and laughter. “It’s kind of an ear worm on steroids,” said Gleason, whose 2017 book “Woman Walk the Line: How the Women in Country Music Changed Our Lives” featured Lee, among others.

The song manages the neat trick of sounding retro yet not dated. Sweet guitar licks snake around Lee’s voice in the original recording. Boots Randolph’s saxophone solo drives it home. The party flies by quickly, the song over in two minutes, six seconds.

Composer Johnny Marks already had some seasonal hits to his credit, including “Rudolph, the Red-Nosed Reindeer” and “A Holly Jolly Christmas.” He specifically sought out Lee for his new song in 1958 and it’s easy to see why: Who better to convey its innocence and spirit than a 13-year-old girl at the forefront of the Baby Boom? Rock ‘n’ roll was in its infancy then, too.

In the song, Lee sings about “mistletoe hung where you can see, every couple tries to stop.”

In real life, she hadn’t experienced her first kiss. “Lord, no,” she said. “Not to say I didn’t want to. I wasn’t even allowed to date until I was 16.”

The song hits plenty of holiday reference points — pumpkin pie, caroling, boughs of holly. You can overlook the part of the chorus that doesn’t make much sense: what is the “new old-fashioned way,” exactly?

The simplicity of “Rockin’ Around the Christmas Tree” is a big part of its appeal, said Nathaniel Sloan, a musicologist at the University of Southern California and co-host of the “Switched on Pop” podcast. Like many successful holiday songs, it evokes nostalgia for a happier, more peaceful time — even if that’s more imagination than reality, he said.

The style is more rockabilly than traditional rock or country, and Sloan believes that has much to do with why it continues to sound fresh.

“The thing that has always stunned me about the song is that you’re listening to a 13-year-old’s performance, and it doesn’t sound that way to me,” he said. “There’s a depth to the vocal, even a weathered quality, that I can’t believe she was so young. It’s pitch-perfect.”