docs: Stick the table headers to the top of table.

Signed-off-by: Tim 'mithro' Ansell <tansell@google.com>
diff --git a/docs/_static/extra.css b/docs/_static/extra.css
index c9b2423..93d4aa8 100644
--- a/docs/_static/extra.css
+++ b/docs/_static/extra.css
@@ -41,3 +41,11 @@
 	white-space: pre;
 	display: inline-block;
 }
+
+.page-content table thead th {
+	position: sticky !important;
+	top: 0;
+	z-index: 2;
+	background-color: #fff;
+	box-shadow: 0 1px 1px -1px rgba(0, 0, 0, 0.4);
+}