Making Windows Themes: Suggestions...

These are three of seven images from the "Good Morning, Good Morning" sequence in "Singing in the Rain" showing Donald O'Connor, Debbie Reynolds, and Gene Kelly doing what they did so well, singing and dancing.

The point I'm taking too long to reach here is that if you play a YouTube Video in full screen mode, and use your screen capture to save images, these will automatically be sized for your monitor screen, and the only editing you will likely need is a little 'auto enhance' or maybe brightness and sharpening.

Then, put them all into a folder you have named DesktopBackground (all one word, because it's a system Dword) and then put that into another folder that you have named with the name of your new theme, in this case 'Good Morning'.
Then, park that on your Desktop. Go into C:\Windows\Users\(your name)\AppData\Local\Microsoft\Windows\Themes and drag you new folder into that Themes folder. Open it, then open the DesktopBackground folder inside, choose Select All from the taskbar, and then right-click one of those selected thumbnails, and choose Set As Desktop Background. Your new theme should now show on the Desktop. Right-click an empty spot on the Desktop and then from the dropdown, choose the bottom selection, Personalize. In that framed area near its top, in the upper left corner, you should see a thumbnail image of your new theme. Right-click that and choose "save" and give it a name - the same one you chose for its main folder a moment ago would be nice. Then down below the framed area, click on the icons for desktop backgrounds and color to complete your selected choices in each of those. Click "Save Changes", and then you're done. Enjoy the new theme.