By default, Windows 10 has a light theme enabled. To enable a dark theme (mode) in Windows 10, you can use several methods: use Windows Settings or make changes in the registry editor.
How to enable Dark Theme in Windows 10 through Windows Settings
First way
This is the easiest way. Click 
Start, then 
Settings, or use the keyboard shortcut + I
In the options window that opens, select Personalization.
Go to Colors and look for the option Choose your color and select Dark.
After that, both the Windows Settings window and the rest of the windows and applications of the system will switch to a dark theme.
Microsoft Store will also switch to a dark theme.
Second way
Right-click on an empty space on the desktop. In the context menu that opens, select Personalize. Further steps are similar to the steps from the first paragraph.
High contrast mode
For people with visual impairments, there is a high contrast mode. To activate it, you need to go to Windows Settings > Ease of Access > High Contrast. Here you can select several high-contrast themes (including light ones).
You can also customize the colors more flexibly.
How to enable Dark Theme in Skype
To turn on the dark theme in Skype, click on the three dots to the right of your profile photo and select Settings from the menu that opens.
Then go to the Appearance section and select the Dark Theme. You can also choose to automatically change the theme depending on the current Windows theme.
How to activate Dark Mode in Windows 10 via Registry Editor
In earlier versions of Windows 10, there was no option to turn on the dark theme in Settings. Therefore, advanced users did it through the registry editor. This method is already outdated, but just in case I will describe it. Suddenly, one of the readers did not update the system and uses the old versions of the “dozens”.
Before using this method, it is highly recommended that you create a Windows 10 restore point.
Press the key combination + R and in the window that opens, enter the word regedit.
In the window that opens, go to the Personalize section. To do this, copy this address into the address bar.
Computer\HKEY_CURRENT_USER\SOFTWARE\Microsoft\Windows\CurrentVersion\Themes\Personalize
Here, right-click on the right side of the window and select New > DWORD (32-bit) Value from the context menu.
Name the newly created setting AppsUseLightTheme and set the value to 0.
In computer science, the number 0 means False, and 1 means True. These are the so-called boolean values.
So we’ve created a setting called “Applications use light theme” and a value of 0 – false, don’t use it.
The changes will take effect immediately.
How to remove dark theme from the registry
To do this, simply remove this parameter or change its value to 1, that is, to True.
