This PR is a follow up of #18815 and #18816, but this time let's migrate
the `supports` theme keys.
Let's imagine you have the following Tailwind CSS v3 configuration:
```ts
export default {
content: ['./src/**/*.html'],
theme: {
extend: {
supports: {
// Automatically handled by bare values (using CSS variable as the value)
foo: 'foo: var(--foo)', // parentheses are optional
bar: '(bar: var(--bar))',
// Not automatically handled because names differ
baz: 'qux: var(--foo)',
// ^^^ ^^^ ← different names
// Custom
grid: 'display: grid',
},
},
},
}
```
Then we would generate the following Tailwind CSS v4 CSS:
```css
@custom-variant supports-baz {
@supports (qux: var(--foo)) {
@slot;
}
}
@custom-variant supports-grid {
@supports (display: grid) {
@slot;
}
}
```
Notice how we didn't generate a custom variant for `data-foo` or
`data-bar` because those are automatically handled by bare values.
I also went with the longer form of `@custom-variant`, we could use the
single selector approach, but that felt less clear to me.
```css
@custom-variant supports-baz (@supports (qux: var(--foo)));
@custom-variant supports-grid (@supports (display: grid));
```
---------
Co-authored-by: Jordan Pittman <thecrypticace@gmail.com>
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