One can always add those stylesheets themselves in their browser, or through the uBlock Origin extension. Otherwise (one of the many darkmode extensions) "Dark Reader" is available for Safari (macOS and iOS), Microsoft Edge, Google Chrome, and Mozilla Firefox (Windows, macOS, Android). On iOS you can also use Firefox (or Brave) that has builtin darkmode for all websites.
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One can always add those stylesheets themselves in their browser, or through the uBlock Origin extension. Otherwise (one of the many darkmode extensions) "Dark Reader" is available for Safari (macOS and iOS), Microsoft Edge, Google Chrome, and Mozilla Firefox (Windows, macOS, Android). On iOS you can also use Firefox (or Brave) that has builtin darkmode for all websites.