Allow @tailwind screens directive inside an at-rule

Author: adamwathan

src/lib/substituteResponsiveAtRules.js

@@ -34,23 +34,23 @@ export default function(config) {
     })
 
     const hasScreenRules = finalRules.some(i => i.nodes.length !== 0)
+
     if (!hasScreenRules) {
       return
     }
 
-    const includesScreensExplicitly = css.some(
-      rule => rule.type === 'atrule' && rule.params === 'screens'
-    )
-
-    if (!includesScreensExplicitly) {
-      css.append(finalRules)
-      return
-    }
+    let includesScreensExplicitly = false
 
     css.walkAtRules('tailwind', atRule => {
       if (atRule.params === 'screens') {
         atRule.replaceWith(finalRules)
+        includesScreensExplicitly = true
       }
     })
+
+    if (!includesScreensExplicitly) {
+      css.append(finalRules)
+      return
+    }
   }
 }