Canonicalization: prevent inlining CSS-wide keywords (#20417)

This PR fixes an issue where canonicalization suggestions in
intellisense result in 'weird' suggestions.

```
The class text-foreground/60 can be written as text-default-soft-hover
```

If we look at the CSS provided by the issue, this doesn't immediately
make sense:
```css
@theme {
  --color-foreground: var(--foreground);
  --color-default-soft-hover: color-mix(in oklab, var(--default) 60%, transparent);
}

:root {
  --foreground: oklch(0.2103 0.0059 285.89); /* near-black */
  --default: oklch(94% 0.001 286.375); /* light gray */
}
```

But it turns out that when you use Uniwind (React Native) with HeroUI,
that the setup looks more like this:
```css
@import 'tailwindcss';

@theme {
  --foreground: unset;
  --default: unset;
}

@theme inline {
  --color-foreground: var(--foreground);
  --color-default-soft-hover: color-mix(in oklab, var(--default) 60%, transparent);
}
```

During the canonicalization step, we inline all the `@theme` values, the
reason for this is that `text-[#fff]` can be turned into `text-white`
even though they look slightly different:
```css
.text-\[\#fff\] {
  color: #fff;
}
.text-white {
  color: var(--color-white, #fff);
}
```

But when we inline them, it looks like this:
```css
.text-\[\#fff\] {
  color: #fff;
}
.text-white {
  color: #fff;
}
```

Internally, we use signatures to make sure that they are safe to be
subtituted with eachother. In this case, the signatures will look like
this:
```css
.x {
  color: #fff;
}
.x {
  color: #fff;
}
```

If we now look at the signatures of the original issue, you would see:
```css
/* text-foreground/60 */
.x {
  color: color-mix(in_oklab,unset_60%,transparent);
}

/* text-default-soft-hover */
.x {
  color: color-mix(in_oklab,unset_60%,transparent);
}
```

That's because the `@theme` variables were inlined, resulting in the
exact same signature, thus we consider them the same.

This PR makes sure to never inline [CSS-wide
keywords](https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/Data_types#css-wide_keywords)
(such as `unset`) and therefore keeping the CSS variable reference:
```css
/* text-foreground/60 */
.x {
  color: color-mix(in_oklab,var(--foreground)_60%,transparent);
}

/* text-default-soft-hover */
.x {
  color: color-mix(in_oklab,var(--default)_60%,transparent);
}
```

Fixes:
tailwindlabs/tailwindcss-intellisense#1610

## Test plan

1. Existing tests pass
2. Added a regression test

Checked manually in the regression repo

Before:
<img width="1358" height="421" alt="image"
src="https://github.com/user-attachments/assets/8ab3de97-17e4-4e11-b335-bb37218ff2ee"
/>

After:
<img width="1177" height="247" alt="image"
src="https://github.com/user-attachments/assets/cbbfcf04-3ed3-4fa7-a3eb-ef607239f4ad"
/>

---------

Co-authored-by: greptile-apps[bot] <165735046+greptile-apps[bot]@users.noreply.github.com>

Author: RobinMalfait

CHANGELOG.md

@@ -28,6 +28,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Skip ignored directories entirely when computing watch globs (`scanner.globs`), instead of walking their full contents on every rebuild ([#20408](https://github.com/tailwindlabs/tailwindcss/pull/20408))
 - Oxide: drop invalid UTF-8 candidates ([#20389](https://github.com/tailwindlabs/tailwindcss/pull/20389))
 - `@tailwindcss/vite` no longer forces a full page reload for external files (e.g.: `.php` files) ([#20414](https://github.com/tailwindlabs/tailwindcss/issues/20414))
+- Canonicalization: don't merge utilities that reference different theme variables set to CSS-wide keywords like `unset` ([#20417](https://github.com/tailwindlabs/tailwindcss/pull/20417))
 
 ## [4.3.3] - 2026-07-16
 

packages/tailwindcss/src/canonicalize-candidates.test.ts

@@ -1638,4 +1638,26 @@ describe('regressions', () => {
       'lg:flex',
     ])
   })
+
+  // https://github.com/tailwindlabs/tailwindcss-intellisense/issues/1610
+  test('does not merge utilities whose theme variables resolve to CSS-wide keywords', async () => {
+    let designSystem = await __unstable__loadDesignSystem(
+      css`
+        @tailwind utilities;
+        @theme {
+          --foreground: unset;
+          --default: unset;
+        }
+        @theme inline {
+          --color-foreground: var(--foreground);
+          --color-default-soft-hover: color-mix(in oklab, var(--default) 60%, transparent);
+        }
+      `,
+      { base: __dirname },
+    )
+
+    expect(
+      designSystem.canonicalizeCandidates(['text-foreground/60', 'text-default-soft-hover']),
+    ).toEqual(['text-foreground/60', 'text-default-soft-hover'])
+  })
 })

packages/tailwindcss/src/canonicalize-candidates.ts

@@ -2563,6 +2563,25 @@ function canonicalizeAst(designSystem: DesignSystem, ast: AstNode[], options: Si
   return ast
 }
 
+// Variables whose theme value is a CSS-wide keyword (e.g.: `unset`) are never
+// inlined. These are typically registered as a placeholder to be re-assigned at
+// runtime, so two variables that share such a value are not interchangeable.
+//
+// E.g.:
+//
+// ```css
+// @theme {
+//   --foreground: unset;
+//   --background: unset;
+// }
+// ```
+//
+// Inlining would make `text-(--foreground)` and `text-(--background)` produce
+// the same signature `color: unset`, even though they are different at runtime.
+//
+// https://developer.mozilla.org/en-US/docs/Web/CSS/Reference/Values/Data_types#css-wide_keywords
+const CSS_WIDE_KEYWORDS = ['initial', 'inherit', 'revert', 'revert-layer', 'revert-rule', 'unset']
+
 // Resolve theme values to their inlined value.
 //
 // E.g.:
@@ -2578,8 +2597,8 @@ function canonicalizeAst(designSystem: DesignSystem, ast: AstNode[], options: Si
 // }
 // ```
 //
-// Which conveniently will be equivalent to: `text-red-500` when we inline
-// the value.
+// Which conveniently will be equivalent to: `text-red-500` when we inline the
+// value.
 //
 // Without inlining:
 // ```css
@@ -2595,13 +2614,13 @@ function canonicalizeAst(designSystem: DesignSystem, ast: AstNode[], options: Si
 // }
 // ```
 //
-// Recently we made sure that utilities like `text-red-500` also generate
-// the fallback value for usage in `@reference` mode.
+// Recently we made sure that utilities like `text-red-500` also generate the
+// fallback value for usage in `@reference` mode.
 //
-// The second assumption is that if you use `var(--key, fallback)` that
-// happens to match a known variable _and_ its inlined value. Then we can
-// replace it with the inlined variable. This allows us to handle custom
-// `@theme` and `@theme inline` definitions.
+// The second assumption is that if you use `var(--key, fallback)` that happens
+// to match a known variable _and_ its inlined value. Then we can replace it
+// with the inlined variable. This allows us to handle custom `@theme` and
+// `@theme inline` definitions.
 function resolveVariablesInValue(value: string, designSystem: DesignSystem): string {
   let changed = false
   let valueAst = ValueParser.parse(value)
@@ -2630,6 +2649,9 @@ function resolveVariablesInValue(value: string, designSystem: DesignSystem): str
     seen.add(variable)
     if (variableValue === undefined) return // Couldn't resolve the variable
 
+    // CSS-wide keywords are never inlined
+    if (CSS_WIDE_KEYWORDS.includes(variableValue.toLowerCase())) return
+
     // Inject variable fallbacks when no fallback is present yet.
     //
     // A fallback could consist of multiple values.