Order summary component using HTML/CSS

I applied other users (precious) advices and used rem units to size my items instead of fixed sized and flex display everywhere. I must say it is much easier and faster this way.

Even though, the site seems to be responsive I would like my main container to fill 80% of the screen wdith wise when on a mobile. I checked on my phone and it's working properly (well, proportion are fine but too small). I have another issue as well with the image. When I sized down the page on my laptop, at a certain point, my main container fills 80% of the screen but the image is slightly shorter (width).

Thanks for reading !