Allow @variant to be used at the top-level (#16129)

This makes it so `@variant` is replaced at the top level and not just
within rules. This also fixes a bug where `@variant` wasn't handled when
inside an `@media` at-rule.

CHANGELOG.md

@@ -21,6 +21,7 @@ and this project adheres to [Semantic Versioning](https://semver.org/spec/v2.0.0
 - Do not emit `@keyframes` in `@theme reference` ([#16120](https://github.com/tailwindlabs/tailwindcss/pull/16120))
 - Discard invalid declarations when parsing CSS ([#16093](https://github.com/tailwindlabs/tailwindcss/pull/16093))
 - Do not emit empty CSS rules and at-rules ([#16121](https://github.com/tailwindlabs/tailwindcss/pull/16121))
+- Handle `@variant` when at the top-level of a stylesheet ([#16129](https://github.com/tailwindlabs/tailwindcss/pull/16129))
 
 ## [4.0.1] - 2025-01-29
 

packages/tailwindcss/src/index.test.ts

@@ -3510,6 +3510,38 @@ describe('@variant', () => {
               background: white;
             }
           }
+
+          @variant hover {
+            @variant landscape {
+              .btn2 {
+                color: red;
+              }
+            }
+          }
+
+          @variant hover {
+            .foo {
+              color: red;
+            }
+            @variant landscape {
+              .bar {
+                color: blue;
+              }
+            }
+            .baz {
+              @variant portrait {
+                color: green;
+              }
+            }
+          }
+
+          @media something {
+            @variant landscape {
+              @page {
+                color: red;
+              }
+            }
+          }
         `,
         [],
       ),
@@ -3522,6 +3554,38 @@ describe('@variant', () => {
         .btn {
           background: #fff;
         }
+      }
+
+      @media (hover: hover) {
+        @media (orientation: landscape) {
+          :scope:hover .btn2 {
+            color: red;
+          }
+        }
+
+        :scope:hover .foo {
+          color: red;
+        }
+
+        @media (orientation: landscape) {
+          :scope:hover .bar {
+            color: #00f;
+          }
+        }
+
+        @media (orientation: portrait) {
+          :scope:hover .baz {
+            color: green;
+          }
+        }
+      }
+
+      @media something {
+        @media (orientation: landscape) {
+          @page {
+            color: red;
+          }
+        }
       }"
     `)
   })

packages/tailwindcss/src/index.ts

@@ -244,6 +244,11 @@ async function parseCss(
               return WalkAction.Stop
             }
           })
+
+          // No `@slot` found, so this is still a regular `@variant` at-rule
+          if (node.name === '@variant') {
+            variantNodes.push(node)
+          }
         }
       }
 
@@ -429,6 +434,13 @@ async function parseCss(
         replaceWith(node.nodes)
       }
 
+      walk(node.nodes, (node) => {
+        if (node.kind !== 'at-rule') return
+        if (node.name !== '@variant') return
+
+        variantNodes.push(node)
+      })
+
       return WalkAction.Skip
     }