use --alpha(color / 50%) instead of --alpha(color, 50%)

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

@@ -12,7 +12,7 @@ describe('--alpha(…)', () => {
     expect(
       await compileCss(css`
         .foo {
-          margin: --alpha(red, 50%);
+          margin: --alpha(red / 50%);
         }
       `),
     ).toMatchInlineSnapshot(`
@@ -30,7 +30,7 @@ describe('--alpha(…)', () => {
         }
       `),
     ).rejects.toThrowErrorMatchingInlineSnapshot(
-      `[Error: The --alpha(…) function requires two arguments, e.g.: \`--alpha(var(--my-color), 50%)\`]`,
+      `[Error: The --alpha(…) function requires a color and an alpha value, e.g.: \`--alpha(var(--my-color) / 50%)\`]`,
     )
   })
 
@@ -42,19 +42,19 @@ describe('--alpha(…)', () => {
         }
       `),
     ).rejects.toThrowErrorMatchingInlineSnapshot(
-      `[Error: The --alpha(…) function requires two arguments, e.g.: \`--alpha(red, 50%)\`]`,
+      `[Error: The --alpha(…) function requires a color and an alpha value, e.g.: \`--alpha(red / 50%)\`]`,
     )
   })
 
   test('--alpha(…) errors multiple arguments are used', async () => {
     expect(() =>
       compileCss(css`
         .foo {
-          margin: --alpha(red, 50%, blue);
+          margin: --alpha(red / 50%, blue);
         }
       `),
     ).rejects.toThrowErrorMatchingInlineSnapshot(
-      `[Error: The --alpha(…) function only accepts two arguments, e.g.: \`--alpha(red, 50%)\`]`,
+      `[Error: The --alpha(…) function only accepts one argument, e.g.: \`--alpha(red / 50%)\`]`,
     )
   })
 })

packages/tailwindcss/src/css-functions.ts

@@ -12,20 +12,22 @@ const functions: Record<string, (designSystem: DesignSystem, ...args: string[])
   theme: legacyTheme,
 }
 
-function alpha(_designSystem: DesignSystem, value: string, alpha: string, ...rest: string[]) {
-  if (!value || !alpha) {
+function alpha(_designSystem: DesignSystem, value: string, ...rest: string[]) {
+  let [color, alpha] = segment(value, '/').map((v) => v.trim())
+
+  if (!color || !alpha) {
     throw new Error(
-      `The --alpha(…) function requires two arguments, e.g.: \`--alpha(${value || 'var(--my-color)'}, ${alpha || '50%'})\``,
+      `The --alpha(…) function requires a color and an alpha value, e.g.: \`--alpha(${color || 'var(--my-color)'} / ${alpha || '50%'})\``,
     )
   }
 
   if (rest.length > 0) {
     throw new Error(
-      `The --alpha(…) function only accepts two arguments, e.g.: \`--alpha(${value || 'var(--my-color)'}, ${alpha || '50%'})\``,
+      `The --alpha(…) function only accepts one argument, e.g.: \`--alpha(${color || 'var(--my-color)'} / ${alpha || '50%'})\``,
     )
   }
 
-  return withAlpha(value, alpha)
+  return withAlpha(color, alpha)
 }
 
 function spacing(designSystem: DesignSystem, value: string, ...rest: string[]) {