Would have to be a very, very, very long video.
I haven't used themes since XP days, when they were great. They were called Msstyles.
The Uxstyle patcher let one use themes, that were not approved by Microsoft.
Tried a few in Windows 8.1 Most could never look right. They became better with lots of registry hack changes.
The problem with that is, it can be difficult to get the modified system files back to normal, usually ending up reformatting drive.
I have used the free Resource Hacker, which works ok in Windows 10, to replace a few of the bitmaps, and png files. Took forever to find the ones to replace. Could never figure out the rest.
From what I've read there are programs to make, and modify theme files. Stardock has had SkinStudio for years. There is another, called Win7 Style Builder. These both cost money, and are no walk in the park. A very steep learning curve. There are probably more.
I think all have instruction tutorials with forums to help.
If you have some artistic skills, with a massive brain for computers skills, no problem.
If you don't, it might be better to start out just modifying the start menu, instead of the thousands of changes in a full blown theme.
Says supports Windows 8 features, so probably ok with Windows 10?
Says with Windows 7 support. Don't know if it can make ones for 8/10?
Edit: I just looked at their forum, and see people like Mr GRiMM (a famous theme maker),
talking about a start menu in Windows 10 section. So I gather program still works in Windows 10.
One can make or modify the start menu, by what is called "skinning"
They say no system files are modified, so it's quite safe to make your own start menu.
The problem with that is, the menu has to follow the contraints of the operating system,
so some properties will not work. There is a learning curve as well. One has to make, or modify bitmaps, as well as changing text in what is called a script. You don't have to know computer coding langauge skills, as it is all in plain English.
It uses that Resource Hacker program to put the english instructions back into computer code for you(complile).
With Windows 10 constantly forcing updates, I'm sure a working theme or just the menu, that one makes today, will get crippled, and not work after a month of updates!