What post editor are you talking about in 2,3,4 points?
After starting Publii, I select Posts at the top of the left hand vertical margin menu (with blue background.) Then I select the Post title. This brings up the post with a minimalist interface. I’m not sure of the name of this post editor.
In terms of responsivity issue: it is affected by your content, not the theme.
That’s interesting. In other words, would you say the inclusion of a Google Chart alters the “responsiveness” of the page? To solve this, should I use a Markdown shortcut such as /embed or /image?