Prepare Grid for the future: CSS Flexbox and CSS Grid

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We need to investigate a few brain minutes to what we do, when CSS flexbox and CSS grid will become usable for all main browsers. Currently Grid is a desktop tool: We can only arrange slots and boxes for desktop purposes. For mobile we just collapse slots underneath each other. Looking at increasing mobile usage that is not really future proof. In the near future it is officially possible to adjust the number of slots to the browser viewport size (it is already possible now with complex CSS or some JavaScript). That is where Grid comes to its limits.

We probably need a deeper concept change away from static container slot appearances. On the one hand Grid users should see how their Grid behaves on different screen sizes (when making the browser window smaller there should be the mobile view). As an idea: The WordPress theme preview allows you to test the theme on desktop, tablet and mobile view, without actually resizing the browser window.
On the other hand we need something like dynamic containers (e.g. mobile 1d1, tablet 1d2-1d2, desktop 1d3-1d3-1d3) or even get away from the container thinking to something like dynamic box placement.
Difficult.