Glass2k is a free application that can set the transparency of any Window.
Glass2k is an older application originally designed for Windows XP, but it worked perfectly for us in Windows 10.
It's very simple to use. By default, if you right-click on any Window, you can quickly change the transparency from 10 percent to 90 percent. There are other additional keyboard shortcuts you can use, but you rarely will need them with the right-click option. You can load Glass2k when Windows starts and auto-remember each Windows chosen transparency settings.
Additionally, you can quickly change the taskbar transparency with a slider.
Glass2k was in beta when it was abandoned, so imagine our surprise at how well it still works. It's free, fast, lightweight and we love it.