Responsive design using flexbox - Four card feature section

I'll appreciate any feedback! I just recognized that the text with the heading is "shaking" a little bit when the animation of the cards play. I don't know why that happens. There is also a problem with the animation of the cards itself. Before the animation the page's height is greater than after it. I am not sure how to prevent this (tried overflow: hidden, but that would also cut out the other content after the animation).