Complete newbie here. I have yet to successfully install and use Linux at all. But I'm intrigued by its flexibility.

I'm a fan of the "classic" Windows (Windows 95-2000) user interface (meaning a launch or menu button in the lower left corner, clock in lower right, app shortcuts and windows across the bottom, menus within windows, open top). Since a lot of what I do is in the Googleverse, I also like the ChromeOS look and feel too.

My wife is stuck on our ChromeBook since our Mac died, but she's still a fan of the MacOSX interface.

I'm aware there are Linux distros and desktop environments that mimic all these:

"Classic" Windows style: Linux Mint, PCLinuxOS KDE, Trisquel, etc.
ChromeOS: Chromixium/Cub Linux, CloudReady
MacOSX: Elementary OS, Peach OSI, Pear/Pearl Linux (dead)

Is there a single distro that can do all three looks? Could I log in to my user account on the computer, see the Windows or ChromeOS style look, log out, and then have my wife log in to her account and see the OSX look?

Even better, is there a way within a single user account to switch easily among looks without logging out? Like workspaces, where a function key or clickable icon would whisk away the Windows look and usher in the ChromeOS look for me, then back again, and similarly for her, to go from the MacOSX look to the ChromeOS look, and back again?

Sorry if this should have been posted in the Distros forum, but if many distros at least have themes that enable different users to have different looks, and this is simply a matter of setting up a given distro properly, then I need to know that. And if it's actually possible to cycle back and forth among entire UIs quickly and easily within a single user account (and I'm not talking about taking 5 minutes each time to drill down into user preferences and select this or that theme), I'd love to know that too.

Any help much appreciated...

The style you're looking for is pretty much what you get with the Xfce or MATE desktop environments. I think KDE is the closest to OSX, but I haven't really seen OSX lately, so I'm not sure. You have to log out to change the desktop environment, AFAIK, but that's not a big deal. You don't have to restart the entire computer, just log out of the current session and log back in either as a different user, different DE, or both. It only takes a few seconds. You probably want to set up different user accounts for you and your wife, and that's easy enough to do. You can install any DE on any distro, and as many DEs as you like. Plus as many user accounts as you like. Linux was designed from the start as a multiuser operating system.

The Windows approach to "user interfaces" was always grounded in "the hardware of the time." That is to say: the operating system always assumed that it had direct access to the physical graphics hardware, and that there was not enough "available, 'spare' capacity" to allow for any alternatives.

Macintosh, on the other hand, "realized that it came from 'Unix == Mach,'" and therefore realized that it must "support both worlds." OS/X therefore supports both "native applications" and "X11."

Linux fully-embraces the "XWindows / XOrg" model: the user-interface is "fully client/server."

Look at Ubuntu MATE set up, in particular the new expected 16.04LTS release with the additional Mutiny interface.
You can do that with any distro but it gives you out of the box experience.

technically speaking, this is possible.
each user would use a different desktop environment.
you would have to set this up yourself.

the bigger problem is to find an equivalent linux desktop environment to each of your 3 choices. there will not be an exact match, and even if the looks are almost the same, functionality will still differ somewhat.

The windowing system that is used in Unix/Linux ... "XWindows" or "XOrg" ... is built of several loosely-coupled software layers, unlike the highly-monolithic design of Microsoft Windows. One of the top-level components is the so-called "Window Manager" or "Desktop," and yes, you can have several of these and you can even switch between them on-the-fly.

Some window-managers are extremely like MS-Windows. (Or, these days, has it become "the other way around?" ... )