This may not be the final version but it is the first version I have got to work, there are some areas that will need attention after the import, the Proper Tree on Windowws 7 uses the following property.

Explorer & Shell > Explorer > ProperTree > Background > FillColorHint

And on Windows 10 and 11 it uses the following properties.

Light Mode > Explorer & Shell > Explorer > Explorer Nav Pane > FillColor
Dark Mode > Explorer & Shell > Explorer > Explorer Nav Pane > FillColor

The same goes for the Reading Pane, Windows 7 uses the following properties.

Explorer & Shell > Explorer > ReadingPane > Background > GradientColor1, 2, 3

And on Windows 10 and 11 it uses the following properties.

Light Mode > Explorer & Shell > Explorer > ReadingPane > Background > FillColor
Dark Mode > Explorer & Shell > Explorer > ReadingPane > Background > FillColor

I don't know of a way to convert those color properties so I have grabbed the colors from a different fill color so have a look at the original colors and make any corrections needed.

You will also need to add the navigation buttons if your Windows 7 theme did not have them.

Also if you want to have custom frames on Windows 11 you will either have to find a way to modify your system files like ミறѳѳղղįզվદ彡 or use Basic Themer2

If the Windows 7 theme does not have matching frames in Windows & Caption Buttons > Basic then you will need to copy them from Windows & Caption Buttons > Aero > DWM Window.

The frames can not use any transparency and must be solid images, if you want some transparency then use System Transparency

When you use Basic Themer I have been using it in the whitelist mode and only adding the things I want it to affect, like explorer.exe for example, first delete all the excluded programs and then add the ones you want and check the Whitelist Mode checkbox.