Add a dummy export statement to files imported as ES modules.

Inside Google, we are making it a requirement for files that are imported using ES syntax to be "marked" with an import or export statement.

Change-Id: I0fd3b2b58cc08c35c156c67edf9323decca3b8d5

src/main/resources/static/styles.js

diff --git a/src/main/resources/static/styles.js b/src/main/resources/static/styles.js
index e93e711..75421fa 100644
--- a/src/main/resources/static/styles.js
+++ b/src/main/resources/static/styles.js
@@ -19,3 +19,5 @@
      </style>
   </template>`;
 styleElement.register('coverage-column-styles');
+
+export {};