Design and Implement macOS 11 Document Icons
By default, if you don’t specify a document icon for a file type in your app, macOS will automatically create one for you by compositing your app’s icon together with the correct extension name. This is a common pattern for imported document types or non-proprietary file formats that your application can open such as MP3, JPG or PNG.
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To create a new custom document icon, you can provide a background fill, center image, or text string. Each of these three elements is optional, allowing you to use just one element or any combination of the three to customize your icon. From there, macOS will automatically layer, position, and mask these elements, then composite them into a page icon with a right corner fold.
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