rothman “Dressing in monochromatic colors is elongating,” says Rothman, in a Diane von Furstenberg dress ($365) and her own jewelry. She assists client Gregory Wright, who wears a Giorgio Armani shirt, jacket and pant ($425, $1,095 and $395), Ferragamo belt ($280) and Canali scarf ($250). (Abby Greenawalt/For Express)

Of all the challenges you encounter at work, deciphering the dress code may be the most perplexing. What, truly, is business casual? Does a gig on the Hill still mean nothing but suits for both sexes and pantyhose for women? D.C. stylist Lauren Rothman (styleauteur.com), who has helped dress everyone from interns to high-level execs, tackles these issues in her new book, “Style Bible: What to Wear to Work” ($23, Bibliomotion).

D.C. has a reputation for being a conservative town. Does that mean our workwear is extra conservative?
This is a city that’s always hungry for more power. And power in D.C. looks different than other cities. In Silicon Valley, power might be jeans and a suit jacket. But if you try to wear that here in a boardroom, it’s not going to work.

What is the biggest workwear no-no?
For women, it’s overexposure. Exposed bra straps, excessive cleavage, visible panty lines. And for men, it’s clothing that’s wrinkled, stained or ripped — the fraternity boy look. Some guys look like they’ve slept in their clothes! Unless you’re on the campaign trail, there’s no reason you should be sleeping in your clothes.

How can women modernize the power suit?
The coordinated set is the new suit. Women can make their own suit by pairing a cream skirt and a cream cashmere sweater.

Is it possible to look sharp and be comfortable at the same time?
Structure to your clothes is what gives you that presentable look. Men’s jackets should not be oversized. I’ll have clients put on blazers and contort their arms to tell me it’s too tight. “Look Lauren! I can’t muscle up my arms and cross them sideways.” And I just ask them if that’s something they need to do at work. Other than shaking hands or doing a half hug or speaking at a podium, you don’t really need to do gymnastics.

Is it appropriate to let your work clothes express your personality?
I think you want to know going into a job how you want to be perceived. Do you want to be seen as a fashion enthusiast or a kooky person who wears a different trend every single day? The latter draws the wrong kind of attention. A great fit and standout accessories will do the opposite.

You encourage readers to dress for the job they want.
I tell my clients to lead in style. You can typically identify who the leader is when you walk into a meeting. So much of that has to do with executive presence. The way you dress should never indicate that you are a level below someone else.

How can men avoid the D.C.“uniform” of khakis and a blue shirt?
Add color. We’ve gotten plenty of private-sector guys who will wear pink and purple. Still, even though brighter colors have gone mainstream, you’d be hard-pressed to find any of that on the Hill.

How lax is too lax for casual Fridays?
The biggest misconception? That casual Friday means you can dress like it’s the weekend. Really, it’s one step down from what you wear Monday through Thursday, and one step up from what you wear on Saturday and Sunday to be with your kids or go to the flea market. You’re not going to the mall or for a drink — you’re still going to work.

Is there a government furlough dress code?
If you want to see the silver lining  of the government shutdown from a fashion perspective, don’t let the work clothes collect up. Use this time to flex your business casual muscles! At first I was seeing a lot of sweatpants, but now people are pairing their blazers with jeans.