I'm also having a issue with custom css properties.

For example, this isn't working:

--paper-input-container-color: red;

I believe this is a problem with Errai because it works properly in the browser's developer console,

but doesn't show up if it is put into a style sheet for a Templated class.

for example: @Templated(provider = HomeTemplateProvider.class, stylesheet = "home.css")

Any media selectors, calc functions, or custom properties in home.css won't work.

They will however work if they are put into the index page, but this is not ideal.