Now I can use this function：
ResourceFunction["DarkMode"] to use the dark mode, but when I turn on Mathematica again, the black mode will not work. How can I set to use the black mode permanently.
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You can change the default stylesheet as follows:
Go to menu: Format > Options Inspector
Set the scope dropdown menu to "Global Preferences"
Download the stylesheet notebook of ResourceFunction@"DarkMode" from here.
DefaultStyleDefinitions path to wherever you saved the notebook.
DefaultStyleDefinitionsback to "Default.nb".