CSS has a neat feature that allows us to test if the browser supports a particular property or property:value combination before applying a block of styles — like how a @media query matches when, say, the width of the browser window is narrower than some specified size and then the CSS within it takes effect. In the same spirit, the CSS inside this feature will take effect when the property:value pair being tested is supported in the current browser. That feature is called @supports and it looks like this:
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For example, iOS shipped support for CSS grid in version 10.2, but iOS has had flexbox support since version 7. That's a decent gap of people with older iOS devices that do support flexbox but not grid. I'm sure there are more example gaps like that, but you probably get the idea.
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JavaScript has an API for this. To test if it exists...
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