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The nice thing about a dress is that most of them can work for both casual and business environments. And, in the summer they're nice and cool. It's relatively the same for skirts- you can get away with a casual shirt if you pair it with a skirt but that doesn't always work with dress pants.
Dress pants also work- pair them with a nice top. But with summer coming, I'm all over the dress/skirt thing.
Here's what I generally do when I start a new job- I dress more formally during the first week (because it's acceptable to be over-dressed but not under-dressed), and watch what other people wear. Then you get a sense of what exactly "business casual" means in that office and you can dress accordingly. I gotta go with dresses/skirts for the first week for you- always fits the office (unless your job involves a lot of bending, standing etc.).