Responsive landing page using flexbox

For responsive images you should look into srcset instead of having two <img> and hiding one with css. When you hide images in css the browser will still load the image, but only show you one. In other words you end up using more bandwidth than if you just sent over the big one and scaled it down.

Instead of "card__left" you should call it "card__image" or similar. Since the image isn't on the left in mobile view "card__left" doesn't make sense anymore, but "card__image" always will.