This is a Windows 10 theme I made for Openbox. I wanted to make my own so I knew it would be as close as possible to Windows 10 using the Openbox theme engine. I believe this is as close as you can get without modifying the source code.

Limitations:
You can't have different settings for the title bar buttons (minimize restore close), so they use the default dark/light blue when hovering which means the red the close button (only) uses had to go (definitely not a good default for all 3).
You can't set the exact size of the buttons or title bar height, this is based on the font size. However, I was able to set padding, etc. so that the official size font (9 pt) looks close.

Tweaks:

Looks best with the official Segoe UI font.
Copy this from:
C:\Windows\Fonts\segoeui.ttf
and
C:\Windows\Fonts\segoeuib.ttf
to
~/.fonts
Then refresh your font cache:
fc-cache -fv
Refer to screenshots for settings in obconf.

Background
Copy the Win10 background from:
C:\Windows\Web\Wallpaper\Windows\img0.jpg
to
~/Pictures/
To set the background, you can't rely on just Xorg, because it doesn't support jpeg images. You have to install something else, e.g. feh
sudo apt install feh
If you don't already have an autostart file for Openbox, create one at:
~/.config/openbox/autostart
Add the following line either way:
feh --bg-scale ~/Pictures/img0.jpg

Enjoy!