Product preview with grid and flex

Feedback on how to remain proper scaling of the container when zooming out would be welcome. (See css file for the problem I had). When I used flex instead of grid, I could not get both divs within the container to be 50/50 in width even after setting 100% on both.

I'm also not entirely sure if the mobile view is good. When I first view mobile view with the emulation mode, it looks bad, but when I get back to desktop view, and then again back to mobile view, it looks well fitted to the screen size.