After World War II, white Americans moved to suburban communities that explicitly barred black people, while many men continued to commute to their jobs in the city. But advances in civil rights, including the Civil Rights Act of 1964, meant that workplaces became increasingly diverse. To this day, many people continue to live in much more racially-segregated areas than where they work.
To illustrate this phenomenon, a journalist at Vox mapped out the populations of American cities (including DC) by racial makeup during the day, when people are working, and at night, once they've gone home. Take a look:
That isn't to say that workplaces are now some utopia of diversity and equal opportunity. When we zoom into workplaces at an individual level, we see that many of them are similarly segregated by race. Even in racially-diverse workplaces, often higher-status workers (like managers) are white, while lower-status workers (like cleaning staff) are people of color.
So why does this racial segregation persist in the places we live and the places we work? That's a topic for another article, but in short: white people in power haven't prioritized dismantling the racist structures that entrenched segregation in the first place. (And it probably doesn't help that a full 75% of white americans only have white friends.)