Don't remove keyframe stops when using important utilities

src/lib/generateRules.js

@@ -118,10 +118,20 @@ function applyImportant(matches, classCandidate) {
 
   let result = []
 
+  function isInKeyframes(rule) {
+    return rule.parent && rule.parent.type === 'atrule' && rule.parent.name === 'keyframes'
+  }
+
   for (let [meta, rule] of matches) {
     let container = postcss.root({ nodes: [rule.clone()] })
 
     container.walkRules((r) => {
+      // Declarations inside keyframes cannot be marked as important
+      // They will be ignored by the browser
+      if (isInKeyframes(r)) {
+        return
+      }
+
       let ast = selectorParser().astSync(r.selector)
 
       // Remove extraneous selectors that do not include the base candidate

tests/important-modifier.test.js

@@ -147,3 +147,32 @@ test('the important modifier works on utilities using :where()', () => {
     `)
   })
 })
+
+test('the important modifier does not break keyframes', () => {
+  let config = {
+    content: [
+      {
+        raw: html` <div class="!animate-pulse"></div> `,
+      },
+    ],
+    corePlugins: { preflight: false },
+  }
+
+  let input = css`
+    @tailwind utilities;
+  `
+
+  return run(input, config).then((result) => {
+    expect(result.css).toMatchFormattedCss(css`
+      @keyframes pulse {
+        50% {
+          opacity: 0.5;
+        }
+      }
+
+      .\!animate-pulse {
+        animation: 2s cubic-bezier(0.4, 0, 0.6, 1) infinite pulse !important;
+      }
+    `)
+  })
+})