Can you view print stylesheets applied directly in the browser?

Yep.
Let’s take a look at how to do it in different browsers. Although note the date of this blog post. This stuff tends to change over time, so if anything here is wrong, let us know and we can update it.
In Firefox…
It’s a little button in DevTools. So easy!
Open DevTools (Command+Option+i)
Go to the “Inspector” tab
Click the little page icon

In Chrome and Edge…
It’s a little weirder, I think, but it’s still a fairly easy thing to do in DevTools.
Open DevTools (Command+Option+i)
If you don’t have the weird-special-bottom-area-thing, press the Escape key
Click the menu icon to choose tabs to open
Select the “Rendering” tab
Scroll to bottom of the “Rendering” tab options
Choose print from the options for Emulate CSS media

In Safari…
Safari has a little button a lot like Firefox, but it looks different.
Open DevTools (Command+Option+i)
Go to the “Inspector” tab
Click the little page icon