chore: Add stylelint

.stylelintrc

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+{
+  "extends": ["stylelint-config-recommended-scss", "stylelint-prettier/recommended"],
+  "rules": {
+    "selector-pseudo-class-no-unknown": [
+      true,
+      {
+        "ignorePseudoClasses": [
+          "global"
+        ]
+      }
+    ],    
+    "@cloudscape-design/license-headers": [
+      true,
+      {
+        "header": "\n Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.\n SPDX-License-Identifier: Apache-2.0\n"
+      }
+    ]
+  },
+  "plugins": ["./build-tools/stylelint"]
+}

build-tools/stylelint/index.js

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+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+import licenseHeaders from "./license-headers.js";
+
+export default [licenseHeaders];

build-tools/stylelint/license-headers.js

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+// Copyright Amazon.com, Inc. or its affiliates. All Rights Reserved.
+// SPDX-License-Identifier: Apache-2.0
+import stylelint from "stylelint";
+
+const ruleName = "@cloudscape-design/license-headers";
+const messages = stylelint.utils.ruleMessages(ruleName, {
+  rejected: "Missing license header",
+});
+
+function licenseHeadersPlugin(enabled, { header }, context) {
+  if (!enabled) {
+    return;
+  }
+
+  if (!header) {
+    throw new Error(`stylelint ${ruleName} rule requires a header option.`);
+  }
+
+  const trimmedHeader = header.trim();
+
+  return (root, result) => {
+    let foundComment = false;
+    let firstComment = null;
+
+    root.walkComments(function (comment) {
+      if (comment.parent.type === "root" && comment === comment.parent.first) {
+        if (!firstComment) {
+          firstComment = comment;
+        }
+
+        if (comment.text.trim() === trimmedHeader) {
+          foundComment = true;
+        }
+      }
+    });
+
+    if (!foundComment) {
+      if (context.fix) {
+        const newComment = `/*${header}*/\n\n`;
+        root.prepend(newComment);
+      } else {
+        stylelint.utils.report({
+          message: messages.rejected,
+          node: firstComment || root,
+          result,
+          ruleName,
+        });
+      }
+    }
+  };
+}
+
+licenseHeadersPlugin.ruleName = ruleName;
+licenseHeadersPlugin.messages = messages;
+
+export default stylelint.createPlugin(ruleName, licenseHeadersPlugin);

build-tools/stylelint/package.json

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+{
+  "type": "module"
+}