Fix opacity modifier using CSS variables

CHANGELOG.md

@@ -32,6 +32,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Rebase `url()` inside imported CSS files when using Vite ([#14877](https://github.com/tailwindlabs/tailwindcss/pull/14877))
 - Ensure that CSS transforms from other Vite plugins correctly work in full builds (e.g. `:deep()` in Vue) ([#14871](https://github.com/tailwindlabs/tailwindcss/pull/14871))
 - Don't unset keys like `--inset-shadow-*` when unsetting keys like `--inset-*` ([#14906](https://github.com/tailwindlabs/tailwindcss/pull/14906))
+- Fix opacity modifier using CSS variables ([#14916](https://github.com/tailwindlabs/tailwindcss/pull/14916))
 - _Upgrade (experimental)_: Install `@tailwindcss/postcss` next to `tailwindcss` ([#14830](https://github.com/tailwindlabs/tailwindcss/pull/14830))
 - _Upgrade (experimental)_: Remove whitespace around `,` separator when print arbitrary values ([#14838](https://github.com/tailwindlabs/tailwindcss/pull/14838))
 - _Upgrade (experimental)_: Fix crash during upgrade when content globs escape root of project ([#14896](https://github.com/tailwindlabs/tailwindcss/pull/14896))

packages/tailwindcss/src/compat/plugin-api.test.ts

@@ -291,7 +291,7 @@ describe('theme', async () => {
         color: color-mix(in oklch, #ef4444 50%, transparent);
       }
       .variable {
-        color: color-mix(in oklch, #ef4444 calc(var(--opacity) * 100%), transparent);
+        color: color-mix(in oklch, #ef4444 var(--opacity), transparent);
       }
       :root {
         --color-red-500: #ef4444;

packages/tailwindcss/src/css-functions.test.ts

@@ -215,7 +215,7 @@ describe('theme function', () => {
           }
 
           .red {
-            color: color-mix(in oklch, red calc(var(--opacity) * 100%), transparent);
+            color: color-mix(in oklch, red var(--opacity), transparent);
           }"
         `)
       })
@@ -237,7 +237,7 @@ describe('theme function', () => {
           }
 
           .red {
-            color: color-mix(in oklch, red calc(var(--opacity, 50%) * 100%), transparent);
+            color: color-mix(in oklch, red var(--opacity, 50%), transparent);
           }"
         `)
       })

packages/tailwindcss/src/utilities.test.ts

@@ -9969,7 +9969,7 @@ test('bg', async () => {
     }
 
     .bg-current\\/\\[var\\(--bg-opacity\\)\\] {
-      background-color: color-mix(in oklch, currentColor calc(var(--bg-opacity) * 100%), transparent);
+      background-color: color-mix(in oklch, currentColor var(--bg-opacity), transparent);
     }
 
     .bg-inherit {

packages/tailwindcss/src/utilities.ts

@@ -112,13 +112,6 @@ export function withAlpha(value: string, alpha: string): string {
     alpha = `${alphaAsNumber * 100}%`
   }
 
-  // If the alpha value is a percentage, we can pass it directly to
-  // `color-mix()`. In any other case, e.g.: `var(…)`, `round(…)`, … we need to
-  // make sure it's a percentage.
-  else if (alpha[alpha.length - 1] !== '%') {
-    alpha = `calc(${alpha} * 100%)`
-  }
-
   return `color-mix(in oklch, ${value} ${alpha}, transparent)`
 }