LOS ANGELES — Whether it’s a gallery party or a casual day of shopping, girls are showing some leg. At a recent San Francisco art opening, ballerina-meets-peasant skirts ruled the evening. Most young ladies paired their mid-calf flounced looks with plain T-shirts or tanks. Meanwhile, on a sunny afternoon on L.A.’s Melrose Avenue, it was all about denim — long, short, sandblasted or deep blue. And studded punk belts, quirky flip-flops or slouchy messenger bags added a personal touch.