Flah card on Smartphone

How can I make flashcards responsive to the size of the screen of a smartphone.
Now it's so small, that you can't see the text of image.
first image on laptop
second image on smartphone

The responsiveness of interactive pages on mobile is not great. I had a very quick look at this, and my initial hacky fix would be something like:

But I hate overriding CSS rules like this, and also it doesn't work perfectly, but it's perhaps a start...