I think it differs from industry to industry and from region to region. You might be allowed to wear whatever you want to work, but it may be held against you when you try to advance in your profession. What's acceptable at a software company in Seattle might be unacceptable at a bank in Des Moines.

In the 1980s, every college grad looking for a corporate job consulted the book Dress for Success. The general rule was to dress for the job to which you aspire. If you were an administrative assistant, you'd dress like a manager. It's different now, of course.