docs: 🐛 css enhancement + add gtag

Signed-off-by: slumbering <slumbering.pierrot@gmail.com>

website/src/theme/Heading/styles.module.css

@@ -0,0 +1,10 @@
+/**
+ * Copyright (c) Facebook, Inc. and its affiliates.
+ *
+ * This source code is licensed under the MIT license found in the
+ * LICENSE file in the root directory of this source tree.
+ */
+
+.enhancedAnchor {
+  top: calc(var(--ifm-navbar-height) * -1 - 0.5rem);
+}