Yep.
1) Selected it through the theme picker after i installed the theme in the C:\Program Files (x86)\GTK2-Runtime\share\themes folder, and the C:\Program Files\GIMP-2\share\themes folder as well.

2)Then i started GIMP. I noticed the metal windows were there but not the correct sliders.

3)So i went to edit>pref>folders>themes and directed GIMP pref to the C:\Program Files (x86)\GTK2-Runtime\share\themes folder.

4)I removed the pref theme folder Gimp had for C:\Users\Rod\AppData\Roaming\GIMP\2.10\themes. It's no longer needed.

5) I restarted Gimp and picked my theme. No problems at all after that.

Now, by the look in the GIMP instalation process image you posted, it seem that GIMP installed in the right place.
1. Now go to: C:\Program Files (x86)\GTK2-Runtime\share\themes Copy the all the Themes.
2. Go to: C:\Program Files\GIMP 2\share\themes and Paste the Themes here
3. Go to: C:\Program Files\GIMP 2\share\gimp\2.0\themes and Paste the Themes there too. That is it.

Try the Selector plck the Theme and. Start GIMP

Just a curiosity (not quite funny):
- my installer (gimp.org) no longer asks for the 'Select installation mode' (maybe it chooses the answer from the previous installation itself);
- allows you to overwrite an older version (without first uninstalling it) with a newer version.

It does ask for installation mode after you choose where to put GIMP's installation. I posted a screenshot somewhere here. It also allows you to overwrite it without uninstalling it.

Been so safe myself, I do uninstall GIMP before I install the newer version so it will start from fresh. In Windows you'll never know how GIMP is going to react. I had user telling me that they installed over the older version and GIMP started to acting up, giving them all kinds of problems.

Now, in your Preferences the themes that are showing are the four Default themes. Now you need to put all those nice themes from: C:\Program Files (x86)\GTK2-Runtime\share\themes folder to your: C:\Program Files\GIMP 2\share\themes and Paste the Themes folder. Do the same putting in: C:\Program Files\GIMP 2\share\gimp\2.0\themes folder.

@Mackenzieh.
Installing Gimp is a separate topic (although there are quite a few of them already).
I wouldn't mention it, but YES - overwriting is bad practice and the "Select Install Mode" option no longer appears at any point during the installation.

It may not appear during installation, but you can select an installation mode after you choose where GIMP will install, so there's that.

@Mackenzieh

I do not want to prolong the discussion not about the post, but I have to repeat:
if I writed that I do not have this option anymore, it means that in this case I also do not have the option to choose the installation location.

This is usually due to the fact some users install files into the main gimp install. Gimp doesn't like that. When it uninstalls it leaves all those files in the main gimp install. Hence you need to go delete them all after uninstall.
If you do not install any other files in the main gimp install directory Gimp uninstalls perfectly.

Like say for instance you throw a couple of dll files into the bin folder and sometime later you uninstall gimp. Then you re install Gimp and you could quite possibly have duplicate library link files. Gimp as we all know doesn't like that either and will cancel both of them out.

That's interesting because you should. I had it when I clicked recommended users and then clicked on customize.
Then when it asks you to where you want GIMP installed, you should see browse, click where you want to put it GIMP. It was obvious to me, that you had it when you posted the screen shot here: viewtopic.php?f=23&t=17035&start=50 (post 57) in order to help me out. That option just doesn't disappear. You could have overlooked it.

Like Rod stated in his last post, GIMP won't install in the right folder GIMP 2 if you have third party item in it and the files stayed. It does not give you the option directory pop up window to choose where to install. It just go right through and chooses any directory and creates another GIMP 2 folder somewhere in your PC.

Really, all the recent statements about the Gimp installation are not confirmed in my case (Windows 10 Home 64bit).
I note that this is not a problem for me - just a curiosity.

I will repeat again:
- I did not uninstall Gimp (I do not recommend this practice) installed in c:\Program Files\GIMP 2;
- I had a lot of my own add-ons (dll and exe);
- when starting the installer in the Customize mode, the following options do not appear: "Select installation mode" and select a place (location);
- the installer itself chose c:\Program Files\GIMP 2.
Therefore, drawing general conclusions from your own installation is not appropriate for others. I believe that it is the existing entries in the Registry that are very important (decisive).