Mariuccia Mandelli, an Italian fashion designer who electrified the runway with short shorts known as “hot pants,” knitwear whimsically emblazoned with animals, and pantsuits for the modern, yet feminine, working woman, died Dec. 6 at her home in Milan. She was 90.

Her death was reported by Corriere della Sera and other Italian media outlets. The cause was not immediately available.

Mandelli was regarded as royalty in Milan, the fashion capital of Italy, for more than half a century. A onetime elementary school teacher, she launched Krizia, her fashion label, in the mid-1950s, drawing its name from a Platonic dialogue about female vanity.

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A decade later, still relatively unknown, she stunned the insular Italian design world by claiming an important fashion prize for a collection presented at the Palazzo Pitti in Florence. The award identified her as both a significant talent and a maverick: Unlike many of her contemporaries, she had eschewed wild colors in favor of black and white.

Blacks, browns and creams — the shades of Italian coffees, the San Francisco Chronicle observed — remained prominent in her palette for years. Her independent streak, likewise, lasted. Umberto Eco, the Italian author and philosopher, quoted in W magazine, observed that Mandelli “invents the taste of her own public.”

She designed clothing for children and for men, and the Krizia line included jewelry, fragrances and Champagne. But she was best known for women’s wear that was seen as contemporary and daring, a reflection of the feminist movement that coincided with Mandelli’s rise as a force in design.

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“Women at the time expressed the will to change the system,” she once told Corriere, an Italian daily. Designers, she said, took their lead. “I tried to liberate women by eliminating what was superfluous, adapting clothing to daily life.”

She used fabrics that were mainstays of men’s clothing, such as pinstripe wools. She favored pants — whether jodhpurs, stirrups or billowy knickers — over the more traditionally feminine skirt. And she made innovative use of pleats to project both power and style.

But she disdained women’s fashion that copied menswear, including the style of pantsuit that was once promoted for career women.

“We are going toward the year 2000 and women should go ahead and not backwards and strike out on their own,” she told The Washington Post in 1984. “To copy mannish clothes is to repeat an error.”

To avoid repeating the error, Mandelli designed a variation on what she considered the stale office uniform for women.

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“She makes a pants suit look soft and gentle by using unconstructed jackets and trousers that fit smoothly across the hips, then widen toward the ankles,” fashion critic Bernadine Morris wrote in The New York Times in 1988. “She experiments with the new knee and below-the-knee lengths in dresses and skirts. . . . In all, Miss Mandelli provides a neat balance between wearable and inventive clothes, and shows Italian fashion at its best.”

In other outfits, she employed sheer fabric —or the absence of fabric — to alluring effect. In the early 1970s, Mandelli helped popularize the so-called hot pants that were distinguishable primarily for how little of the leg they covered.

Particularly recognizable was her knitwear — the sweaters that featured a menagerie of animals, including cats, parakeets, squirrels, foxes, horses, crocodiles, pandas, monkeys, giraffes, leopards, tigers, lions and elephants. (The Krizia headquarters was across the street from Milan’s zoo.)

Mariuccia Mandelli was born in Bergamo on Jan. 31, 1925. She recalled that she was 7 when she began making clothing for her doll, Corriere reported.

She found an early mentor in an acquaintance who ran a tailoring shop and who told Ms. Mandelli’s mother not to send the girl to the university because she would one day become a giant of fashion.

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Mandelli studied in Switzerland and worked for a time as an elementary teacher before venturing into fashion, first sewing simple dresses and skirts with a friend.

In the 1990s, amid the Clean Hands investigation that revealed widespread corruption in Italian government, Mandelli was found to have paid a bribe to tax officials, who she claimed had strong-armed the money from her with threats to delay production at her workshops. Her conviction was later overturned.

Shenzhen Marisfrolg Fashion Co., a Chinese manufacturer of apparel, bought Krizia in 2014.

Survivors include her husband and business partner, Aldo Pinto. A complete list of survivors was not immediately available.

Reflecting on her work, and on the gender politics of her era, Mandelli once remarked that “it is rather useless and a bit ridiculous to dress like a man to bolster your position.” It was also, she seemed to think, a bit uncomfortable.

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“I’ve always asked myself how a man goes back to wearing a suit and tie after a vacation at the beach,” she told an interviewer in 1992. “To wear a buttoned-up collar with a tie all day is like wearing armor.”

For men, she designed outfits that she hoped would be more comfortable, including a cashmere sweater that she compared to “wearing a kitten.”