Add GitHub Actions workflows

.github/workflows/lint.yml

@@ -0,0 +1,28 @@
+name: Lint
+
+on:
+  - push
+  - pull_request
+
+jobs:
+  lint:
+    name: Lint
+    runs-on: ubuntu-latest
+
+    steps:
+      - name: Check out Git repository
+        uses: actions/checkout@v2
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v1
+        with:
+          node-version: 12
+
+      - name: Install dependencies
+        run: yarn install
+
+      - name: Lint
+        run: |
+          yarn lint:css
+          yarn lint:ts
+          yarn format

.github/workflows/test.yml

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+name: Test
+
+on:
+  - push
+  - pull_request
+
+jobs:
+  test:
+    name: Test
+    runs-on: ${{ matrix.os }}
+
+    strategy:
+      matrix:
+        os: [macos-latest, ubuntu-latest, windows-latest]
+
+    steps:
+      - name: Check out Git repository
+        uses: actions/checkout@v2
+
+      - name: Set up Node.js
+        uses: actions/setup-node@v1
+        with:
+          node-version: 12
+
+      - name: Install dependencies
+        run: yarn install
+
+      - name: Run tests
+        run: yarn test