Create shared style to ensure design coherence

[rgreinho]

Issue Type

• Feature request

Expected Behavior

Style that are common throughout the application should be shared between the elements.

Current Behavior

There is no real style sharing implemented. The shared-styles.html file might give you an idea of the goal to reach.

Possible Solution

Follow this guide: https://www.polymer-project.org/2.0/docs/devguide/style-shadow-dom#share-styles-between-elements

[rgreinho]

This will be done as part of PR #39.