Step 1: Download favorite dark theme.
Step 2: Create a folder as “themes” in “C:\Program Files (x86)\Notepad++”
Step 3: Drag and drop the downloaded .XML theme into the new “themes” folder.
Step 4: Open Notepad++ application and go to setting > Click on “Style Configuration”.
Step 5: The downloaded theme will be appear in “select theme” drop down list box.
Step 6: Select the theme and click on “save and close” button, the theme will be applied.