“I’m happy! It’s spring!” said Stella McCartney, without a trace of cynicism, even though the weather gods had looked most unfavorably on her garden party held Monday night in a very rainy New York. Still, McCartney partied on. “Spring is the season to celebrate fashion and life and enjoy,” she said. “We wanted to have a little moment of fun.” The collection was sporty and chic but never too serious, as McCartney combined elegant volumes and top-notch fabric development — see python-embossed jacquards for day and evening and luxurious duchesse satin for cocktail — with wit. There were matchstick, lip and heart motifs, a particularly alluring example coming via a simple, short white dress done in green and navy lace embroideries in the shape of hearts. For daywear, the palette was soft with pale pink, yellow and beige-based florals giving a springtime girlishness to McCartney’s signature tailoring. A slim-fit tailored coatdress came in pinkish snake-print jacquard and a blush Neoprene baseball jacket and matching track pant trod the sexy, sophisticated side of athletic influence.