Default background rendering has to be handled on the button renderer level
because of a specific markup for Outlook (bgcolor attribute). Default text color and paddings are
handled via CSS inlining. That's why they are tested in RendererTest
I used the same background color and font color as the one defined for the button
element in WP core theme.json, and I also used similar padding values
(In core they use "calc(0.667em + 2px) calc(1.333em + 2px)")
[MAILPOET-5814]
codeception/verify 2.1 removed support for expect()->stringContainsString() so we need
to replace it with verify()->stringContainsString().
[MAILPOET-5664]
I envision the StylesController as the source of information about
styles settings in both the editor and renderer.
We will add email styles settings and these will be accessed in PHP via this service.
[MAILPOET-5540]
