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This main site theme applies to your entire site, except for the Refined pages, spaces and projects that have their own specific theme set (see the paragraph below).
Go to the Site Builder.
Click on the name of your current theme, located in the block with your site’s name in it.
Select a theme.
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Customize the look of specific Refined pages, spaces and projects.
In the Site Builder, click on the item's Cogwheel > Settings.
Click on the theme name.
Click the Change Theme button.
Select a theme.
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